What's wrong with "rim protector"? It's more specific than "defensive big man" because some players are good at one-on-one defense or picking up rebounds but not necessarily altering or blocking shots on drives/shots around the basket. To me, that sounds like a very specific skill that statisticians have noticed to be an important part of having a good defense. Especially in today's NBA where teams rarely post up anymore, being a good one-on-one big defender like Perk isn't as critical a skill as it used to be.
I don't see anything wrong with 3 and D either. It's a valuable role player to have on a good team because it complements star wing players. On offense, having 3 pt. range creates enough spacing for your PG and star wing to operate. On defense, guarding the opposing team's best player lets your star conserve energy for his offensive game.
Obviously in a perfect world you'd have five all-stars all with multiple skills but how realistic is that? There are a lot of guys coming into the NBA who are athletic but find that they'll never have the handle or body control to be a force on offense. However, if they can practice this one skill of shooting 3s they can carve out a niche for themselves on a good team. Take Bruce Bowen for example. Guy was useless on offense in Boston, but developed a 3 pt. shot and fit into a role in SA.
Every team is different, but generally speaking, defensive players who can develop that shot can fit into a role in a lot of teams' lineups.