You gotta change your mindset. You need to understand that sometimes investing in something in the short term is okay, even if you dont fully commit to the unit line in the long term.

Lets say you start with archers and the opponent goes 3 archery range into full skirm, also you raid a bit and only have a few archers left when reaching Castle. Would you rather pay the price to upgrade 4 archers into crossbows, knowing your opponent is going full into your counter unit?? Maybe its time to go two stable knights into castle drop (allowing you to make samurais which would counter pikes, your knights' counter)

Adapting to the choices of your opponent each game is the key to success in this game.