The positon of the modification cost squad upgrade causes some not so nice flow of the upgrade system at the moment. Due to it branching out from the +3 weapon upgrade you usually have to make 4 squad upgrades before doing any weapon upgrades and then you’ll do 2 at the same time immediately. Then you’ll only have to do one squad upgrade for the next weapon upgrade.
My suggestion is swapping it with the position of the weapon selling upgrade. This would mean you’ll have to get 3 squad upgrades before making the first weapon upgrade and then 1 squad upgrade each for the other weapon upgrades. This would improve the flow of the weapon upgrades.
Same should be done for vehicle upgrades.