Last time I played a huge random map, an enemy TEC faction was stomping all over the other AI in its region by spamming Hoshikos, and Percherons. When I made contact with him, even a well supported group of 40 gardas bolted onto my main attack fleet couldn't break through his fighter/bomber screens. My attack ships couldn't touch his relatively few attack ships since they were supported by the Hoshiko spam. There were times in those battles were I was confused about what to attack first, The Hoshikos seemed like a good first target but with them self-repairing and supporting each other it would take outrageous amounts of time to destroy them, even with my massed fighter groups, which were getting shredded by his squads. Meanwhile, his bombers would cut apart my attack ships. If I attacked the Percherons first, same difference, as I couldn't destroy enough of them to really make a difference before I had to withdraw. I could go for his low-level cap-ships and force him to withdraw, but he'd just retreat to his heavily populated adjacent territories, which had numbers too large to approach, as I was also fighting another faction at the opposite end of my empire with a sizable fleet. We stalemated, and i eventually quit that game...
That's the only time I've encountered a troublesome AI fleet, mostly because his local dominance allowed him to mass such outrageous numbers of support spam, and there was constant trickle of replacement ships coming from his core worlds.
I should have made a bee-line for his core to wreck his economy, just ignoring our frontier, but I was rowed out with him.
