They want to avoid having too many options to start. If Rome opens upIt needs not be perfectly balanced, but we know for a fact they don't want too many options per civs (despite people somehow ignoring that part again and again), and I would add that I strongly suspect they want more than one path into each civ, so it will likely be close to balance anyway. The idea of ancient civs with 5 or 6 paths so we can overload on later ages is one I would call extremely unsound, as appealing as some of you seem to find it.
Again, we're looking at around as many or more civ after around one year as Civ VI had in its entire existence; and still manny more years of support after, and given Ancient is the first age of the game (and thus the first age of a full campaign they're certainly not going to shaft it on civ count - they'll want a wide variety of civilizations there, so people have lots of options to start the game. They're not going to out all the options later and just players to start with a micro list.
Which, considering the limited selection of ancient civs in large parts of the world (anywhere but Europe, the Middle East, India and East Asia), due tomlimited informstion, is going to be preeeetty hard to do with only five Euros in the long run.
Norman
Spain
HRE
Dutch
Italian CS
Byzantines
… that won’t be too much because if you have 30 Exploration Civs you will probably unlock several by gameplay without trying.
Remember… they limited it because they didn’t want you having to sort through ALL the civs every single time…. if there are some of the civs you Can’t pick, then they have simplified it.
If you have 30 civs per era, I would expect the average base game civ to be unlocking 4 or so. (some like Rome would be higher)
Once you chose a DLC civ though, I would expect many to only unlock 1 civ.