Lol taking both stabs. I'm pretty sure raichu gets ohko'd by hjk even while resisting.
Assuming alolan raichu doesn't get any defense buffs...
252+ Atk Pure Power Mega Medicham High Jump Kick vs. 0 HP / 0 Def Raichu: 627-738 (240.2 - 282.7%) -- guaranteed OHKO
240.2-287%/2 = 119.9 - 141.3%
It ain't even taking an ice punch
252+ Atk Pure Power Mega Medicham Ice Punch vs. 0 HP / 0 Def Raichu: 242-285 (92.7 - 109.1%) -- 56.3% chance to OHKO
Yeah, no. Unless they buff raichu's stats, there's no way in hell I see Raichu being good. it's definitely gonna be better, just not as much as your making it out to be.