hmmm this is a tricky one. I've been away for a while, but I've played this game plenty to know a lot about fortresses and what they're capable of.
I'd say I agree to come up with something more inventive for 75%. Killing fortresses is a grind most of the time and hardly any fun. However... I've experienced a few cases where even a simple mk I fort could be a hell to take out, bombers or not. Imagine an AI world with only 2 wormholes, both very close to the fort. The fort being protected by a forcefield, lots of shield bearers and anti bomber stuff (fighters and bulletproofs in particular). Oh and there were 3 ion cannons too, one of them being mk V. It took me at least 45 minutes to neuter that world and it was not a boring fight, it was a lot of fun actually. destroying that world was a real puzzle. I believe this was at an early-ish 7/7 game, though I'm not sure.
I guess I'm just worried a bit that if we change forts to much, rare-ish cases like this could be impossible to get by.