The Pokmon's staying power can be attributed to its unique combination of design, thematic consistency, and its effectiveness in battle
Mono Red and Izzet Prowess have benefitted from a slow accumulation of excellent low cost spells over several MTG sets: while Cori-steel Cutter is plain cracked, it's the sheer volume of high quality cards laser-focused on an aggro strategy that mean these decks are dominating standard
Later on, as the Oathkeeper may get less useful due to opponents having more mana, he can be traded in to resurrect a planeswalker to the battlefield
Note: You dont have to cast a card for its prowl cost if you dont want to
There may be some deckbuilding tension at some point between effects that are maximized by sacirificing him, sure, but in a 100-card singleton format, that limit will be difficult to determine and it feels that we arent quite there yet