While we're at it, let's combine Protoss shield and ground armor upgrades as well. Ground armor will upgrade ground shields, and air armor will upgrade air shields.
In fact, let's take away everything that made each race's upgrades unique.
A bit of sarcasm there, sorry, but I'm firmly against these cheap kinds of changes rather than addressing the problems more directly.
Terrans upgrades are blatantly underpowered compared to Protoss. +1 armor for Protoss benefits every single ground composition the race has, allowing mindless and easy transitions throughout the game. If you really want upgraded air as well, you get the shield upgrade which benefits "everything" and air armor and attack upgrades from a cybercore, you get at the start of the game anyway.
It's obvious Terran upgrades need a rework for mech to become viable, just the questions if these ones are the correct method.
It's the the upgrades that are the problem, it's the unit interactions we have.