Nothing wrong with doing assistance exercises to get your deadlift & squat up.
In fact, I did not deadlift at all (other than testing 1RM) for the last two months and my DL went up 22.5kg. All due to my assistance exercises.
Right now I can only do a handful of Ab Wheel kneeling roll-outs. If I can do say 3x10 standing roll-outs, I'm sure my squat and deadlift would skyrocket without me training much in those lifts. That bloody Ab Wheel hits your entire torso like nothing else.
If you're familiar with Ross Training, the guy is a 170lbs trainer of fighters. He trains with kettlebells, AbWheels, picking up kegs, sandbags etc. and doesn't deadlift. In a challenge a few years back, he was told that his training can't compare to someone who deadlifts 130kg. Ross picked up 495lbs, almost 3x BW, on the first day of trying.
There are many ways to improve your lifts, other than just doing those lifts.