Then I realized the opponets power forward was 6'1.
Which means it's not very quick to train him further in inside skills. A player's height does not affect their performance in games.
there should be some way to see that he is a great INSIDE defender but a crap outside one. Then I could actually game plan.
You can evaluate the defensive contribution of a single player by looking at the team ratings, tactics, and the individual ratings. The player rating heavily depends on their defensive abilities/contribution. So, a guy who goes 1-10 and gets zero rebounds may have as high a rating as a guy who goes 7-10 and gets 3 rebounds with same minutes. This suggest he played better defence.
It's obviously not very simple, but you should get a good feel after a couple of games.