Yeah and in my experience the maxim isn't even worth building. I was really hurting for suppression in one game though, we got beat by blobs. Is isu worth building? It would fit a guards heavy strategy, since guards are pretty static and long range as well (they get 2 mosins firing on the move lol).
I think the ISU works well because, yes as you said its long-range and it forces the other player to be aggressive, which works with guards defensiveness. It also works well (in theory) because in order to take the ISU out they have to dive, which is where the guards can plink away at their tanks and slow them down etc. That combo alone wont stop a good dive however.
ISU could also be good because this is a very manpower heavy strat and you might not be able to afford to spam t-34's.
Try experimenting with the Quad half-track behind guards/your line to stop too much blobbing.
Also Elephant can counter the ISU pretty easily and your guards wont be too effective vs that...