I like the future paradox pokemon more than the past paradox pokemon for the exact same reason people dislike the future ones, just reversed
A common argument is that the future paradox pokemon are just robot versions of already existing pokemon but that can also be applied to the past ones
"The past paradox pokemon are just primordial/dinosaur versions of already existsing pokemon"
Both groups have designs that are not large departures from the base mon, but it does feel like there are more future paradoxes whose designs feel too close to the originals. This is particularly highlighted so far by Walking Wake, Raging Bolt being very different in design from Suicune and Raikou, while Iron Leaves and Iron Crown do look adhere pretty closely to Virizion and Cobalion. That doesn't mean they are bad designs, per se, but I think people in general like it more when the deviations are substantial.
My initial impression of the paradoxes based on the leak dex images and menu icons was that the past paradoxes were more different than the future paradoxes. Having now used most of them in game my impression is not as lopsided, but I do still give the past paradoxes an edge for differing more from their base forms.
My detailed assessments:

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: I feel like Iron Treads deviates from Donphan more than Great Tusk here, and is typical of some of the changes that I wish were more prominent in the other future paradoxes, as they were creative with the body plan (the tread trunk draping from the back over the face as opposed to being a nose, and giving treads the domed LED face). At first I wasn't as keen on Great Tusk, which did just look like "dinosaur" Donphan to me, but it grew on me a lot. Having more color helped, I think. Overall I like both, but in terms of assessing deviations I'll give
1 point future, 0 points past.

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: My first impression of these was that Slither Wing was way cooler than Iron Moth, being a kaiju-esque mutant of volcarona crossed with larvesta, while Iron Moth looked more like a straight robot conversion of Volcarona. The jet-pack on Iron Moth is a nice touch, but in terms of deviation from base form I would still give
0 points to future and 1 point to past. This said, I've grown to really like Iron Moth, and while I still like Slither Wing's design, the fact that it is bug fighting instead of bug dragon really lets it down.

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: This one does feel pretty close to base form, earning
0 points on that front, though I think a lot of people give it bonus points for being a paradox of an NFE mon.

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: Bonnet being a weird dinosaur-mushroom hybrid definitely earns it a point for deviation from base form for me. Originally it looked like it was going to be Amoongus with mossy hair and spiky... 'hands', but when it turned out to have a centaur-dinosaur thing going on I'd say that was enough to get
1 point.

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: when this first leaked it was after we got to see roaring moon's dex image and a few of the other paradoxes that were bigger deviations in design, so I was a bit disappointed in it. Since seeing it in game and being able to make out the feather-texture on its mane-arm(?), my opinion is that it's more of a subtle variation but still one that I really like and Flutter Mane is my favorite gen 9 mon (though I wish it had fangs instead of a snaggle tooth). But, in terms of distance from the base form I'll give it
0 points.

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: I am not a big fan of sandy shocks, but I will definitely give it
1 point for being a wacky take on Magneton.

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: The first image of this to leak was the dex image, which looked amazing. Major improvement over Salamence and Mega Salamence, which I never cared for. After that things kind of went downhill: the menu sprites and art do not do roaring moon justice. I'd say my impression of the deviation from mega mence has diminished somewhat, but I'd still give this
1 point.

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: As mentioned above, great example of deviation from base form. Going from quadruped to raptor is an inspired design choice. Improves on the design of a Pokemon that I never cared for.
1 point.
:raging_bolt: vs

: Again, I love that Raikou got turned into a brontosaurus. I wish they changed its head up a bit more like they did for Wake, but it still earns
1 point.

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: At first this looked like a more or less straight up robot conversion, but where bundle shines are its animations, having the ejectable head and similar effect for the tail. I do really like it now, but in terms of deviations I will give it only
0.5 points since without the animations it does look like a robot conversion played straight.

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: I saw the menu sprite for this first and was definitely underwhelmed with how little it changed from Hariyama, a mon that I don't care much for. I've warmed up to it since then. Hands does improve of one of Hariyama's weakest points -- its stupid ears -- and the floating hands are a nice touch. Overall, a good design and an improvement on the original mon, but relative to some of the others I'll give it
0 points.

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: Another one where I saw the menu sprite first and was underwhelmed. After seeing it in game, I do appreciate the LED face a lot -- it's used better on Jugulus than most future paradoxes, where the LED on faces are mostly black screens with LED eyes -- and the detached arms are again a nice touch, but it really does just look a lot like robot Hydreigon.
0 points. If they had gone in a direction more like the original tank design Sugimori talked about in an interview, maybe the deviation would have been bigger.

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I love Iron Thorns, but it is really just robot Tyranitar.
0 points. The electric-crystal back spikes are a nice touch, at least.

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: I will give Valiant
1 point, though that's largely because it's a mix of Gardevoir and Gallade's features, so it comes off as a big deviation compared pairwise to each of the base inspirations. At first I thought it was not as good as Roaring Moon, and I still feel like its face looks a bit too much like Mecha Sonic's, but now I would say I probably prefer Valiant over Roaring Moon.

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: As said, seems like a straight robot conversion. It's not bad, but not as inspired as Walking Wake, even when taking into account the neck blades that you only see in animations.
0 points.
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: Again, just not as cool of a design remix as Raging Bolt, even taking into account the horn blades that are sadly also only visible during animations.
0 points.
Lastly, I could compare the Raidons to Cyclizar, but being box legends they both had a lot of care put into their designs, so in terms of deviations they would both get a point so I may as well not count them. I will say that overall I did like Koraidon better than Miraidon, though both are great designs. Miraidon's flaws are its ear wings in glide mode are meh, whereas Koraidon's head-wings are excellent. And then in battle mode Miraidon's serpentine body and jet engines on its thighs put it in an unfortunate design category shared with Palkia.
So, tallying everything up, in terms of deviation from base form I gave the past paradoxes a total of 6/9 points, and the future paradoxes a total of 2.5/9 points.
That said, a lot of the mons I gave 0 points to are mons whose designs I still really like, and its also worth noting that if all of the paradoxes were suicune -> walking wake style remixes, then it would probably feel less impactful overall, so more tame redesigns like Flutter Mane and Iron Moth are welcome. It's just that the future paradoxes feel like they could have used a few more big twists.