I feel your pain, my ships aren't even close to matching what yours are so I try a couple times and then quit. The fact that the fleet AI is controlling Mace's ship is the trouble. I've seen his ship in this challenge use special abilities 3-4 times in a row after one of his ships goes. The fleet AI cheats, even in the fleet arena.
At the same time, "recommended, isn't." is something I've said many times on these forums. It'd be one thing if they just said, "hey you need level 85 and gear 11 and so on" but for so many events and challenges, its just, "oh level 70 can do this!" while you get demolished with max toons. The problem with Mace is that his valour reduces cooldowns 'too much' in this event, so you might never get to see all your reinforcements come out (while he keeps magically sending out ships from his stock of 100 of each type.)
I'd say that's what keeps me the most frustrated and upset about this game, that recommended truly isn't what you need, but at the same time, there's not much effort to fix that problem. I don't care if it is challenging (though this challenge seems over the top), but the "Select Number Generator" (RNG should be called SNG because the programmers input 'select' numbers to pop up with certain percentages, it isn't as random as you'd think), favors the AI far more than it should in these kinds of events with way too small a factor of the player getting the completion. (And some people saying, "its EZ Bro! I finished it the second time I tried with level 50 ships and no mods on my pilots and with one hand tied behind my back, walking uphill on ice..." sure doesn't help the morale of so many who struggle with it.) The answer shouldn't be, "just auto it 400 times and you'll complete it, maybe."
Good luck though, hopefully we all complete it soon enough.