Well, according to their BSTs (Base Stat Totals), Gardevoir's BST is 518 and Weavile's BST is 510.
Based on stats:
Weavile has more HP than Gardevoir (70 vs 68).
Weavile is stronger in Attack than Gardevoir is (120 vs 65).
Their Defense of 65 is the same.
Gardevoir is stronger in Special Attack than Weavile is (125 vs 45).
Gardevoir is stronger in Special Defense than Weavile is (115 vs 85).
Weavile is faster than Gardevoir (125 vs 80).
By type, Weavile (Dark/Ice) has 5 weaknesses (4x weak to Fighting ; 2x weak to Fire, Bug, Rock, and Steel), whereas Gardevoir (Psychic) only has 3 weaknesses (2x weak to Bug, Ghost, and Dark).
Gardevoir can learn Normal-, Grass-, and Psychic-type moves through level up.
Also, she can learn Normal-, Electric-, Grass-, Fighting-, Ghost-, and Psychic-type moves as TMs.
Weavile can learn Normal-, Ice-, Fighting-, Dark-, and Steel-type moves through level up.
Also, he can learn Normal-, Water-, Ice-, Fighting-, Poison-, Flying-, Psychic-, Bug-, Ghost-, and Dark-type moves as TMs.
Stats-wise Weavile tops Gardevoir in HP, Attack, and Speed. Even though Weavile has 5 weaknesses, it can learn a more diverse set of moves in its movepool than Gardevoir can ever learn.