I agree 100% with you - at the moment it seems the AI's are building at random - surely a logical building pattern is to secure defence and then protect economy in that order... a typical AI will have majority level 3 provinces at start of the game with at least 1 at level 7 (the capital) and maybe 2 or 3 other at level 4. It is therefore save to assume that they will only have 3 building grounds for all of their province with the exception of the capital.

I for one would like to see an AI focus on - Infrastructure, Market and Barracks considering that Trading Companies and Colonial Office should in theory ONLY be build in Colonies...

well with colonial troops eventually becoming the strongest units in the game, and mercs the quickest to produce at the start, and barracks needed for that extra manpower the AI's building isn't as flawed as you may think someone did a test where they built economically, another where they went colonial and the 3rd they left it to the AI all tests were done against a full AI contingent and after 2 weeks the AI nation was the most robust out of the 3 giving the most res and had a lot of spare rest to play with it had the biggest army the works

As far as I know the ai does not know how to focus on one tech tree [for troops upgrades].. and dips into them all.

A player can upgrade troops specifically and Vs ai with sporadically upgraded mix of unit types, a player can OWN the larger ai armies [the upgraded tech on specific unit types makes them ALOT more effective]

I think Preventing ai from building more than one kind unit producing build per prov would make for better conquered provinces for players expanding into ai nations.

ofc adding an option to demolish and re-use the limited building slots would work too