1) There was a fix to flying units
here, that caused this new behavior you describe. In short, units only become active when the drop is complete, but flying units became active before they were dropped and that caused some other problems. I fixed them only becoming active when the drop was complete, but then indeed that was very annoying since they drop so slowly. But, after
this build they drop more quickly so it should be ok now. Be sure to check on a version after that to see if it's ok for you. The delay on dropping the flying units is still a bit more then dropping non-flying units, but I think it's ok now. Let me know if you disagree.
2) This is indeed changed, this is 'fixed' behavior. There was a bug in the original game, that made some function in 'gaining negative anger' impossible, this was on functions like getting paid on payday or getting hand paid, units would get 0 happiness. But apparently Bullfrog noticed this too, so for hand paying they added another check that then just reset ALL anger to 0 even if you gave a unit just 1 gold. This is of course completely imbalanced if you can mistreat units a lot and can completely solve it with minimal gold. Now, you need to pay better attention to your units need.
This is fixed now, and units actually gain happiness on payday now. Dropping gold on them, they will gain happiness as they would from getting paid, on a per gold basis. So if you drop 2 paydays worth of gold on a unit, it will gain 4 paydays gold worth of happiness. If you drop 10 gold on a very upset reaper(which takes big paydays), the happiness gain would be negligible. The picked up from gold sound they make sounds a bit bigger or smaller depending on if you give more or small in relation to their payday.
I believe on Ancient Keeper I have enabled classic bug mode to get the old bug back, so there the gold dropping should be the same as before.
3) I have made no on-purpose changes to this. As far as I know this has always been a bit finicky, but if you think the behavior is different now it would help if you can give me some indication around what time you noticed a difference. If horny has gone livid, that's when he will fight friendly units, he cannot be made happy again.