In-game Pokemon are far different than movie portrayals of the Pocket monsters.
Mewtwo in the movie was too mentally powerful for Wargreymon.
It's even more ridiculous that some people think any digimon can stand a chance against movie Arceus. Arceus with all his plates is invulnerable.
Ask that again when Digimon has any of the Milleniummon's (special mention to the reality warper Zeedmilleniummon), multiple god-like Digimon themselves (Yggdrasil, Huanglongmon and the other four Soveirgns, Shakamon, etc.), Bagramon, Lucemon, etc.
Granted, I do think Mewtwo would beat Wargreymon (barely, but still) but lets not pretend that Digimon doesn't have a ridiculous arsenal of overpowered creatures that could easily have Arceus run with his tail between his legs.