What can be done about AI homeworlds (and Mk. IV and "core" planets to a lesser extent)?
Now, the idea that the AI goes heavy in defending its most important stuff, and "all-out" in defending its home, IMO, should be a thing that stays. But the problem is that, due to the simplistic nature of the combat model, there wasn't much you could do in terms of dealing with heavily defended areas beyond "throw more ships at it". (Well, later mechanics made it "do fancy thing, and then throw more ships at it" (tactical warhead use, transports, splitting armies based on bonuses), but you never got rid of the "throw more ships at it" part of it).
This often made the AI homeworld degenerate into an unfun grind to deal with, building and rebuilding entire armies, doing a "fancy thing" to make only a small-ish amount of progress, rince; repeat.
Are there any ideas about how this situation could be improved, without making AI homeworlds any easier or less menacing? Again, I feel that some level of grind should be required; this is the AI going "all-out" in defense. But the current situation seems to get excessive, especially if the RNG arranges things in just the wrong ways.