Yeah Harrison Barnes is much better than Tristan Thompson. Not even close.
Absolutely. That would be worthy of a first rounder as an upgrade.
Walker/Brown/Barnes/Tatum/R.Williams + Pritchard/Smart/Langford/Nesmith/Ojeleye/Theis
is a rotation where the Celtics will have a big advantage again on the wing over any team. During the playoffs you can shorten that to 9 guys, where you only play 2 of Pritchard/Langford/Nesmith/Ojeleye based on performances, roles, needs and situations.