Jacozilla:
As for upgrades, I think CiV had a great idea, but I think BE has a better one. Powerful individual upgrades allowed you both to have everything at once and devalued the nature of unique units. A Cho Ku No is significantly less unique when all your Crossbowmen in every game have that upgrade at the start of medieval anyway. March Riflemen are less unique when every Rifleman that comes out the gate can get March.
Limiting powerful ability upgrades to specific Civs allows for a greater difference in feel on the tactical map. When I see a Dragoon, I don't need to mouse over it to know that it's probably going to be bad for my cities.
Focusing on this portion of your reply now - I'm really not sure how your own logic here applies.
You seem to be saying
a) powerful individual upgrades devalue the nature of unique units (cho ku nu v crossbowman with range +1 promo example)
and
b) limiting powerful ability upgrades to specific civs is a good thing
Let's take A) this is not a equivalent comparison - you're comparing a heavily promoted crossbowman that you'd need to earn on each and every crossbowman by actual action vs just being born with it - vs - a rookie cho ku nu.
I get what you're saying in a general sense, but if you're going to compare equivalently, it wouldn't be a crossbowman with +1 range that is the same as a cho ku no, the more accurate comparison would be a crossbowman with +1 range vs cho ku no with double attack AND +1 range.
Because in the time the crossbowman force is earning their +1 range, the cho ku nu force is getting ready to double attack you in the face, from artillery range. Therefore the individual unit upgrade did NOT devalue the unique unit. It in fact makes the unique unit even more unique and powerful if it can branch path into promotions that supplement what it already gets for free as a unique unit
Now take B) - in BE there are no powerful upgrades to specific civs (aka sponsors), something which I would like ala CiV (e.g. Carolina's march infantry, dutch beggars, etc)
Any sponsor/civ in BE can take any affinity, which is where you get the semi-sort of unique upgrades. Many of the affinity units actually share similar promotion upgrades (20% next to a unit, 30% when attacking ,etc.
It is only a very few actual unique to affinity unit abilities unlocked at higher levels - e.g. supremacy seraphs with x2 intercept, vindicator transport, harmory artillery, etc
Aside from all that though, I don't see how allow different veteran branch promotion paths ( 2 main paths per veteran levels) as well as the 2 main paths per affinity tier 1-4 unlock wouldn't add to the greater difference in feel on the tactical map you said would be good.
If I'm playing harmony and the AI has supremacy with seraphs - like your dragoon example I know that's going to be bad for my air cover, with their double intercepts. But if those seraphs also have veteran promotions that further add to their uniqueness, that would be even more bad - let's say seraphs that intercept twice (via affinity) and have +2 range via veteran levels.
The tactical nature of surprise is a key factor we all want from the AI. We all hate the same old AI scenario. Right now, take the seraph example again - without veteran promos, as bad as I may think double intercept seraphs are, I know that EVERY seraph - his, mine, everyones - has the exact same range, exact same combat power, exact same everything.
I really don't see how addition of veteran branch promo paths would no anything but ADD to the uniqueness of units you face in the field.