Many flying school owners are crooks, but not all. In fact there are some pretty excellent schools out there.
90 minute slots can work, but they rely on everything running properly. Anything less is just asking for trouble and is actually less efficient for all concerned.
Fatigue and low morale go hand in hand. If you try and do 7 days a week (as I have found to my cost) you just end up doing a rubbish job and get totally stressed and knackered for no reason.
Whilst I break this rule regularily, I try and keep all my FI's to 4 hours a day airborne. Luckily as we all have other forms of income, we aren't reliant on doing 7 hours a day to keep the wolf from the door.
FI's do need an association or union purely for them, but with the way the market is at the moment, salaries are only going to go up from here anyway. A simple case of supply and demand.