Yeah, if we're after depth, it makes much more sense to go for Benrahma than Grealish. Both same age, outperformed Grealish in championship last season and is really good technically. In fact, he greatly outperformed Grealish statistically last season despite Villa being the better team and better attacking side.
In fact, apart from end product, here are dribbling statistics in the Championship last season
Benrahma - 2.4 per game, 3.3 per 90 min, 3.3 per 6.5 attempts
Grealish - 1.8 per game, 1.8 per 90 min, 1.8 per 2.8 attempts