would it cause big imbalances to always use the same mix grip without alternating the arms between underhand and overhand? i'm not going to do this, im just curious. my grip sometimes sucks on rows at the last reps, maybe hook grip could fix this or i should do some exercises for my grip, but this would be isolation work hehehe.
My own developing theory is that lifting weights reveals the asymmetries you already have, while possibly creating new ones.
So in my case I have some pre-existing difference between my two shoulders, and a significant strength difference left-to-right from toe to finger. If I open up my left hand on a deadlift my shoulder will be killing me within a half hour, but when I open up my right hand there is no problem. This is despite the fact that I've gone far heavier for many months opening my right than I ever went opening my left. If my body were perfect I could switch off, but it is not so I cannot.
I used to go double overhand for warm-ups and then switch to mixed for the top set but I don't do that anymore, because if I warm up with a different action than the top set then its not really a warm up. I can move more weight if I use the same motion from first to last. Some will object that doing an overhand grip is better for building grip strenght to which I respond: to what end?
If grip is a problem on rows then do more rows. Personally I would not sacrifice my deadlift and its benefits to legs and back over an insistence on one kind of grip or another.