People still don't realize how strong Vega is because he has a lean build. His hands are huge and his functional strength is off the charts. His balance and core strength are top notch as well. And his cardio is second to none.
The only ways to beat him are A) at his own game, or B) lightning quick duckunders + blast doubles if you can get him off balance.
The only guy that could train Mendez for Vega is unfortunately a *too old, not flexible enough, not enough cardio anymore Jaggers. I'm sure he did all he could, but the training partners for a guy like that don't exactly grow on trees.