Am I missing something here? Did the Electric Surge/Surge Surfer combo get banned? How is Alolan Raichu unviable in a meta where Tapu Koko is number 1 in usage? That'd be like Kingdra being unviable in a metagame where Politoed is everywhere (and the Swift Swim combo is legal). Tapu Koko is already stupidly good, and Alolan Raichu effectively forms a double type core to spam down their checks, and he has coverage that does pretty damn well against a lot of those options, with Grass Knot, Psychic for Poison types, Surf for Rain, and Focus Blast for Ttar and such. Alolan Raichu might be in a better place than Kingdra in that regard, since he's fast enough to function without the Terrain, he and Koko can both be Volt-Turners, and Rain's always an option to shit on Alolan Marowak. Is it because the Tapus are all fighting for Terrain or something?
I absolutely agree with all of this. For some reason people seem to think that just because Tapu Koko is the most used Electric type, that it's automatically the best one. This is not true, and in fact I think A-Raichu wins a 1-v-1 between the two due to outspeeding in E-Terrain and Psychic/Psyshock hitting harder (to say nothing of pairing the two as pika pal mentioned). Tapu Koko doesn't invalidate A-Raichu, just like I don't think it'll invalidate M-Mane whenever it is made available. Mega-Venusaur didn't invalidate Amoonguss last gen either as both sat in OU. I don't see A-Raichu dropping.I would like to point out in regards to Alolan-Raichu that it's actually a nice lure for a multitude of Ground type Pokemon due to it getting access to Surf (so many OHKOs on Lando-T's switching in, I don't even know where to begin). I think despite its underwhelming physical Defense and mediocre Special Attack, it has a solid place in OU due to its arguably better typing, nice STAB combination, great movepool (not just coverage wise, but also due to access to tools like Nasty Plot), and high speed with its niche ability Surge Surfer being very abusable due to the ridiculously high presence of Tapu Koko.