In that case why not let Imperialism remove that half XP from purchases? Did Civilizing Mission get nerfed or something 'cause that's how I bought and upgraded most of my units, not whatever per turn gold I got. I fully agree with Owl that the scaler should be changed.
That could work too. I think my suggestion at the end of my post is what I'll stand by, but let me hear your specific proposals.
Well, since G is apparently gonna take a look at Puppet penalties, I think Owl's suggestion for scaling puppet production could work. Even if they're not worth keeping as a puppet you can at least rely on them to build up a solid infrastructure before annexing. Quickly readied cities are very nice for steady lategame conquering.
Healing is the most underperforming ability for the Admiral. Buff healing: more range, let healed units move again, gain yields for the action, something that is noticeable.
Stalker0 is right, Imperialism is also about controlling waters. Use Lighthouses, Harbors and Seaports. You need those buildings for military naval purchases.
Good. Make it so an Imperialist sets maritime bases and then launches attacks on nearby cities. Buff pioneers, by the way.
Puppets are sad because they develop very slowly, that's the source for their unhappiness.
Why not more simple? -30% war weariness. Period.
1- I think that we need to determine is Imperialism is only worthwhile for navy and naval control, or if we should make it useful for land military as well. Tu clearly wants to buff it's naval strengths, I want to shore up it's land weaknesses.
There is still a point to the middle age branches. Fealty is loosely religious. Statecraft is heavily CS focused, which can work for multiple victory types but is best for diplomatic. Artistry is great person focused, which still lends itself a bit more for culture victories.
Not putting all eggs in the same basket.
I got a bit excited thinking about a GA that could support a fleet with some healing and I forgot about the no new code rule, my bad on that one. I'll try to think of something else that is closer to existing mechanics.
Except real colonies didn't develop slower than the main country, nor stay crappy. That was part of the problem for England at least.
America and Canada aren't particularly good examples of colonialism. Think British India, Dutch Indonesia, French Indochina, the Belgian Congo. America, Canada, Australia and to a lesser extent South Africa are less traditional colonialism and more ethnic replacement. It was meant as a sort of callback to mercantilism which saw foreign holdings impoverished and stripped of wealth for the benefit of the mother country.
Do you need to teach the AI to use it? Since Great Admirals already give an aura buff, which they should already know how to use.
If you want it to enhance warmongering with a 'bit' more emphasis on maritime bonuses why are you suggesting adding another bonus to ships?
maintenance. (swap no gold maintenance on garrisons to the authority tree.)
/
yields per turn in unoccupied cities. (puppeted cities stay crappy, but buff the original cities of the empire, just like real colonialism 
)
unhappiness from Puppet cities
/
to Constabularies (moved from Martial law)
Faith
