The thing is, Multi-HW is about tradeoffs.
Notably, as you increase the number of HW you start with, you are making the early game easier at the expense of making the late game harder.
Now, I don't play Multi-HW so this is all theory craft, but I know the AI gets more waves when there are multi-HW, I assume it also gets more reinforcements as well.
The increased reinforcements is where the harder late game comes in. Early game before the reinforcements really start to have an effect, multi-HW lets you walk all over the AI. However in mid to late game you should start running into planets that are sufficiently reinforced to be a challenge, even on multi-HW. (Or it should in how I envision multi-HW balance working.)
The other big thing that makes Multi-HW easier is the extra knowledge you get, but I'm not sure I want to mess with that formula.
Lastly, how similar do we want to keep the multiplayer and multi-HW mechanics?
Hmmm, what about messing with AIP? The biggest advantage multi-HW has is the more territory you start with, without incurring any sort of AIP cost.
No real suggestions in here I realize, but my thoughts on what could be looked at for this.
D.