I don't think authority is really as "feast or famine" as you say. There's always going to be either a nearby civ to conquer or (if the map has the civs more spread out) barb camps. If a player chooses not to use raging barbs, then the lack of on-kill yields is their fault. Even still, I think it's fitting authority would be feast-or-famine because the whole point of the tree is to be more rewarding to the competent warmonger, while being more punishing than progress for those who aren't competent at it
As far as the changes go:
Opener: I don't think the extra experience is worthwhile especially when most of it's going to spearmen which are made obsolete by swordsmen very quickly. The +25% versus barbs suits authority better as it means you can solo farm camps with warriors up until the barbs get spears.
Tribute: This seems dangerously like a buff to authority, something that it really does not need as the best ancient era tree. Either way though, the 25% culture from tribute was pretty worthless in the majority of my games (because of how low yield it is, how unreliable city state locations can be, and because it's better just to go conquering instead of tributing) so I think it's an improvement for usability's sake.
Imperium: moving the +1 happiness to monuments is a huge buff as now you don't have to have a troop using supply pop early game to be able to get happiness. The practical effect of this is that you can far more easily overwhelm other civs, and it also is a factor in making authority a "progress but better" tree. It also stacks the left side of the tree even more heavily, taking away any real reason to go to the right side first, which is just bad design.
Militarism: Decent change. The road maintenance reduction is busted and served (in combination with the tribute policy doubling on finisher) to make authority unironically better as far as infrastructure goes than progress because of how much gold (and production) you get from the policy(s). I think the free unit at 5 is not a good idea because of the reasons I listed in imperium, but I do think it would be better if it was one free unit at 7-8 and then let that no-supply-use promotion carry over on unit upgrade to serve as a small nerf and make it so you don't have to keep un-upgraded units as garrisons to keep the supply-free promotion.
Honor: I don't mind the pop modifier being moved, so no comment.
As far as the changes go:
Opener: I don't think the extra experience is worthwhile especially when most of it's going to spearmen which are made obsolete by swordsmen very quickly. The +25% versus barbs suits authority better as it means you can solo farm camps with warriors up until the barbs get spears.
Tribute: This seems dangerously like a buff to authority, something that it really does not need as the best ancient era tree. Either way though, the 25% culture from tribute was pretty worthless in the majority of my games (because of how low yield it is, how unreliable city state locations can be, and because it's better just to go conquering instead of tributing) so I think it's an improvement for usability's sake.
Imperium: moving the +1 happiness to monuments is a huge buff as now you don't have to have a troop using supply pop early game to be able to get happiness. The practical effect of this is that you can far more easily overwhelm other civs, and it also is a factor in making authority a "progress but better" tree. It also stacks the left side of the tree even more heavily, taking away any real reason to go to the right side first, which is just bad design.
Militarism: Decent change. The road maintenance reduction is busted and served (in combination with the tribute policy doubling on finisher) to make authority unironically better as far as infrastructure goes than progress because of how much gold (and production) you get from the policy(s). I think the free unit at 5 is not a good idea because of the reasons I listed in imperium, but I do think it would be better if it was one free unit at 7-8 and then let that no-supply-use promotion carry over on unit upgrade to serve as a small nerf and make it so you don't have to keep un-upgraded units as garrisons to keep the supply-free promotion.
Honor: I don't mind the pop modifier being moved, so no comment.