dont forget the brokeness of amnesia something only psychics learn.
The fact that Special Attack & Special Defense were one stat (turning Amnesia into Nasty Plot + Amnesia) is a big reason why they were OP. The biggest reason, though, was that they had no real weaknesses. Ghost only had Lick to hit SE (Night Shade is fixed damage). Bug only had Pin Missile and Twineedle, with the latter being on a Poison Type and the former being on a special-based Eeveelution.
Not to mention that Alakazam outsped most of the meta at the time...
Skyrim is the girl who keeps breaking my heart, yet is so hot I still keep coming back on the chance I may get to sleep with her again. - Spurner