Some types of legal work are bog standard paperwork, but the kind of stuff the big firms tends not to be. It takes about 5-6 years for a transactional person to be able to run a small deal by themselves. In litigation it's even steeper. At big firms, most associates (even 8 years in) probably couldn't run a complex case. And the older partners just have better judgement and wisdom that only comes with doing something many times.
But with stuff like writing wills, drafting simple contracts, entity formation, patent applications, etc. tend to have a shorter learning curve.