Fighting unit promotions

[LukeHro]

I was wondering if you guys get to the top promotions for fighting units. On harder difficulties or how?
I play on prince, large map, continents, normal speed. Got my share of barbarians and about 4 cities conquered (not aiming for conquest victory), I never lost a single fighting unit the whole game and still didn't got past second level promotions.
I even took the Aztec capital of size ~15 and 2 other smaller Norway cities with a single bomber, just moving a tank for the final conquest and that bomber just got a single promotion.
So, what needs to be done in order to get to the top promotions? Are they any good anyway?
What needs a bomber to do for example to get to the top promotion despite what I sayed in the prev paragraph, could there ever be so much targets for it in a game unless you absurdly play just for that goal?

 

[kaspergm]

I frequently, if not always, get a couple of units to the top promotion. They are really good, in fact even better than Civ5 double attack, because it doesn't seem to count movement in the normal way when you make the attack, which means you can generally get to use the second attack also, even when I feel movement should allow it. It helps to make combat during the early government which give you extra experience, and notice that fighting barbarians only gives poor experience after the first promotion.

I generally do hate how the promotion trees are designed, however. It feels like I always are forced to pick one or two crap promotions if I want to go to the bottom level.