Well I believe the 990 (kind of an economy version) and even more so the JD 1070 (more a deluxe version) were some of the the biggest heaviest "classified as compact" tractors to ever be offered. The 1070 even had draft control for the 3 point hitch for plowing. Might be the only compact tractor that I have ever seen draft control feature offered on as most compacts only have position control and some of the real cheapies even that position control does not work all that great. There was a time that I really wanted to own a JD 1070 (just too expensive for my needs back when they were new - might be more affordable now as used).
Anyway, You easily have enough hp if you pick the right small square baler. Doing just a few acres the tractor will likely hold up fine. Start covering many acres though and the the PTO driveline strength will likely come into play in a typical lightweight compact even if it has the hp. A 990 or 1070 being a little larger and heavier than the typical compact then it might have a little more strength in the PTO driveline (not sure). Regardless, there is a reason that I think almost every manufacturer has a "voids the warranty clause" on their compact tractors if you hook it to a baler. I am sure their testing likely shows failure problems. A baler is a herky jerky type load on the PTO. No problem on bigger tractors with lots of steel to absorb that herky jerky action even if they are low hp.
So the catch 22 is you are likely fine on just a few acres, but doing hay on only a few acres is rarely profitable or worthwhile (from a cost/benefit perspective). Try to cover a lot of acres with a compact tractor to make doing hay more feasible, justifiable, and profitable then your lightweight tractor will likely not hold up.
I have hobby hayed for quite a few years with a lightweight Kubota L285 (pics on this sight even). It actually handles the baler pretty darn good and the Kubota's choice of slow gear speeds is wonderful. Would I do 25 acres with it? No way as I really like the little tractor and want to keep it nice. The baler now goes on a clunker Farmall h or Farmall M. Nearly a Zero chance the baler will hurt either of those old heavy clunker Farmall's. The Farmall h even has less hp than the Kubota but it does have more torque, mass, and PTO driveline strength.