One of the most annoying things is engines going out. Why? Well other than being unable to move, it...takes freaken forever to rebuild. You can understand it on large heavy engines but on some of the light ones...it takes a long time to bring them back up. Time which takes engineers away from balloons or hulls.
Squid is probably the biggest example of why the rebuild times suck and have sucked for awhile. It has quad and losing 1 engine out literally disables the entire ship. Often times you have to pre-rebuild engines then wait for the 2nd barrage to put them all up and hope the ship can recover. Just usually with only 3 engines up and not at full power, it is futile. However, often by this time balloon or other components are completely gone.
Other ships...I've been on too many Pyras where they lose engines and the amount of dmg coming in makes it impossible to rebuild. You go to rebuild and then the armor is gone/etc. Just about every ship goes through this.
So how many seconds should be acceptable? I remember when this was tweaked long ago. Guns and engines took all day to rebuild. That was tweaked back and it got slightly better. Only bring it up now because with Minotaur and the changes we have currently. Engines feel even more important. Having them remain up can decide if a ship is able to counter a Mino or not.
The disable meta only got stronger. It's traditional counter was kill meta or evasion. Well, Pyra is now nerfed to hell so that is out. Junker is a big blender liability. Squid still can't turn worth a damn and it's engines are far too weak when hit. Spire is possibly the only viable option right now but even that is Jack bait.
Engines able to rebuild faster would help a lot.