Those prints look horrible! The tonality is way off and I can see the grain from a mile away. At that size, you should only be making contact prints!
Seriously, what's the reason this person says you should only be printing from 4x5 (or larger) even at a 8x10 print size? IMO that's pure snobbery. Respect or not, everyone's standards are different and this person just wants you to conform to theirs.
Do YOU like your work?
Should you print 16x20's from 35mm? Maybe not, but if you really want a 16x20 of something you shot on 35mm, then by all means print it.