We're a better defensive team this year than last year. You need to look at ranking within team and not raw data.
A guy who is...
Relatively bad on a good team.
...can be better than a guy who is...
Relatively good on a bad team.
Barttovik has our adjusted defensive efficiency this year as #26 nationally.
We were #108 last season.
I do not know how you improve so much if one guy is really dragging it down.
Jacobson might not be what Lard is on the boards and with rim protection, but he is fundamentally solid with positioning, waiting for the help, and not losing track of his man. He has some capacity to switch on the outside to guard stretch types and wings, and he is smart about recovering and switching back to the big when he has a chance to do so.
Lard and Solo got hosed last year when they were away from the paint, on the other hand.
You are right it is an ecosystem, but Jacobson plays well within it. I am not sure an aggressive rim protector, even a good one, is quite as good of a fit.