Other teams that play with true 4s are going to have that guy guarding one of our guards >=20 feet from the basket? I'll take that trade all day every day. I think our primary concern is big depth for foul purposes as you point out with Leron, matchups secondary as you point out with Finke.
Also defensively, a guard is probably able to apply pressure with quickness at a greater level than a big in general. This will help us apply better ball pressure all over the court and be able to really go for deflections and get out in passing lanes. The defensive trade-offs aren't all bad.