Oh, and added to this, the kickstart should've been cartridge based, so it could easily be replaced.
I can't agree with that notion. It would have greatly increased the cost of buying a new kickstart ROM, relied on some dodgy edge connector that may end up having flaky contacts and the like.
Besides, changing the kickstart chips aren't exactly difficult on most amigas, since they are socketed and generally fairly easy to access, even on wedge models.