I would question that. To be somehow effective with maxims and not get overhelmed by flanks you have to keep them together. So you are loosing a lot of map control.
A combo of Sturmpioneers and Kubels does well vs maxims which will get outmanoeuvred.
I think we may be thinking about different game modes in which case nvm.
Speaking from 3v3+, there are many lane-y maps such as Redball, Across the Rhine (not Ettelbruck surprisingly), Arnhem where flanks are simply impractical/easy to stop. With three Maxims, you can have one covering the flank and 2 for the front, resulting in a practically uncrackable defence before ISGs arrive. Ostheer ally mortars can be matched with teammate mortars and heaven help you if they have a Sniper in all of this.
This doesn't take into account the teammate getting an MG either.