I think that the *time* it takes to build units is fine, just the maintenance that is bad.
Meanwhile, buildings should both be more meaningful and take longer to build (at least the early game buildings).
--> Now some buildings imho already take too long to build, (at least for what they are worth), but in general I think buildings should be something you need to invest in.
(I'm not sure ... maybe investment should be Governors that increase building times, as well as a Mason's Guild)
But thus far I don't see units needing to be built any faster ... we have enough production as it is, just not enough *early taxes* to pay for those units.
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Another thing I would be interested in seeing (at least to see how it goes) would be allowing a stack to take in more units.
Say, with max tech having 12 total units possible in an army. Possibly with 1 Champion for free in a "leadership" slot.
Not sure how the breakdown would be ... maybe start out with 1 leader slot + 6 unit slots. upgraded to 1/7, then 1/8, then 1/10 ... and then the last two upgrades would be 1 leader slot +12 unit slots and then 2 leader slots +12 unit slots. (for stacking leader bonuses)
That way, those that don't focus on leader bonuses can completely skip the last one (that unlocks two leader slots) unless they just want an extra champion in the mix.