I've proposed to update them to mud-brick walls (for relevant civs), but stone walls would also do, I wonder why this is not already the case.    I think this should be the default mechanism, no tech needed (unless there's some strong historical reason). Some have proposed some timer for the engine to be useful after capture, but I don't see this as too different from a longer capture time. Ideally, the default operators should be killed before the engine can be captured, and a mechanism of how to replace them implemented, to fulfil the "timer" role more realistically and separately from the capture itself, and avoid constant switching. This is basically the "base garrison" idea I've proposed before (although I've argued that capture points wouldn't even be needed in that case, to simplify things).

If you want you can try to finish some of the 70% done new animals here are a few https://gitea.wildfiregames.com/0ad/0ad/issues/1983 https://gitea.wildfiregames.com/0ad/0ad/issues/1993 https://gitea.wildfiregames.com/0ad/0ad/issues/2003 there's most of the info in the forum post that the issue links to.

@wowgetoffyourcellphone

Perhaps some technology could be implemented to create a mechanism to prevent  from switching sides constantly.

Yeah, I think being able to capture and use enemy siege machines (I don't know about building them) would balance their damage and health. Or maybe making them less resistant to Pierce damage. You can only have one hero at a time, I've never seen this as a problem. Their supposed to be OP. I think both are good ideas, Fanatics are WAY too resistant for being naked (IMO, they should have almost no resistance, but tons of damage), and champ cav maybe could be slowed down/more expensive. I play MP pretty frequently, (not on the scale that I know others do though), and I personally have only ever found Elephants OP. Walls are broken in general, but the best fix to this is to make palisades only build able in owned territory, and to maybe allow them to upgrade to real walls when those are unlocked. This would mean the player wouldn't have to delete them, making real walls more valuable as well.