Hydra needs to be shortened
Yes, there are a million ways to make autobattle on Hydra better. But at the end of the day, even if they do make those fixes - the fight itself won't become any shorter. On hard, the fight will easily last an hour or more, and using all three keys is just silly if you want to actually try to maximize your damage by trying to run on manual.
The better solution (of course with the autobattle fixes still a requirement) is simply to shorten the fight. I don't have an exact rule to apply here, but my first guess would be to change the max turn count from 1500 to 300, and to have the devour counter start at 10 instead of at 20. All the first half of the fight demonstrates right now, is your ability to understand the mechanics. Beyond that, it's just repetition until the last half of the fight, when the devour counter starts getting low enough to matter. So, short-circuit that process and start it off right there.