The problem is "top of the line" changes as time advances. I often have Dreadnoughts before I can build Battle Cruisers in fact, so it is hard to say whether or not the event was completely unbalanced with the limited information at hand. Generally speaking, if you don't have access to Battleships by 2285 on a large/huge/gigantic map, you may wish to adjust your research priorities the next time around.

As far as the 86 Battle Cruisers go, I believe a decent 10 system empire should be able to weather the storm by. If you can just assemble a stack of 5 on your frontline planet and the AI doesn't attack with all 86 units in a single turn, you can probably defeat 20-30 Cruisers on the first battle, then kill off a steady stream of 10-20 Cruisers per each ensuing turn, depending on the level of your repair tech. Keep in mind that the game heavily favors defensive units in most early encounters. An orbital 4/5 Battle Axe will fight as if it were a 6/5 unit on defense, and they are a lot more durable than Battle Cruisers too. I would suggest you pursue a defensive tactic next time you get hit with such an event and see how it turns out instead.

Edit Paragraph #2: ... should be able to weather the storm by turtling with Battle Axes.

I love the random events, but a few of them can be way out of hand. This is a good example of that.

olaf