I disagree that talking about the Brummbär is irrelevant. They are similar enough to paint a picture, however cost is a part of that picture and maybe a bump in cost for the isu is required for the boons it has. But again, I think looking at the commanders so that the isu can't counter its counters and picking it means missing out on something else is the best start point.
+1
I think the doctrine being able to delete it's counters is arguably the biggest thing about the 152. Lefh can't displace the unit in its deployed area nor put pressure on its repairs because it gets deleted with a click. Not saying that an lefh is a counter but it can help with scattering a line for everything else.
Add guards, mark target, bombing run. Completely stupid not to pick it. 152 doesn't need a cost increase or really anything else on its own, but the shit around it does.