>>43635202Gardevoir is just a less optimized Alakazam.
Alakazam has better special attack and speed.
Gardevoir has better bulk and better physical attack, but that doesn't even matter for a frail special attacker.
Neither of them are surviving many hits, but Alakazam will at least move first against far more opponents and deal more damage, increasing the likelihood of a OHKO and negating the need to take a hit at all.
And even if push comes to shove and they do have to take hits, Alakazam has fewer weaknesses and access to Recover.