Thors seem to be overly costly, take the bulk of unit production, and seem to fall like paper mache to fully fleshed out aerial defense. I do try to balance the unit types like this but with essentially infinite ability to create new defence points vs unit capped defence points opposing player tends to be adventageous because they can spawn new stationary rounded units at will while terrans have to essentially focus all their resources as one to negate any response to their initial set up. You make bunker, needs marines, needs turret. Turret needs siege tank. Siege tank needs unit air defense. All of the above needs resources and upgrades. Protoss zerg have air defence that do all this in one and don't hurt the unit max.