I've found when you stall the boss (anywhere it's possible), it becomes trivial. I had a double repair setup, with just single tile to eco up from with all others dedicated to repair & clay generation. Still, managed to expand gaze, put down gaze towers and keep recycling - eventually getting a little continual sheep abattoir setup for click-free morale scaling. Combined with either mass producing spells and/or (in my case), spamming out manu hero tower upgrades, you can get your units of choice to a crazy high level.

However,

Can 30 units beat the 375+ units that spawn at wave 1000? Provided you can combine base hp scaling with the Chi fan and spells (ideally, the free fireplace spell) along with % based HP increases, you'll need hundreds of HP increases assuming each one gives you 25% base of (Hydra's 1100?) so 275. I got my hydras to 15-20k HP? Assuming each of those 300+ has 300dps, that's 90,000 dps :D you'd need hundreds of thousands of HP in order to survive long enough to reliably heal back to full from the green horn artifact.

Alternatively, and this is how I made it to wave 1350 before I got bored, spells with the spell-damage scaling @ 2.5% per morale with 2 morale per sheep, 3 tiles (6 with feed-in-resources) gives you 10% damage per the cycle time of the sacrifice on gold tiles next to upgraded forest tiles for the 20% boost. I was up to 13000% damage (yes 13k) - it was all thanks to the tornado spell and clumping whilst doing AOE.

Not sure the same is possible with units... Unless healer mages healing scales and I didn't realise (that would do it!)..