I find the ground combat is this mod to be quite rich and rewarding. There is lots of strategy and the units are mostly not redundant (I only play rebels). The only slightly redundant units I would argue are the tier two and tier 3 gunner infantry and basic infantry, which end up being very similar in my opinion (but should still be there for build structure flexibility and flavor logic). Other than that, every unit fills a fairly distinct role.

As far as vehicles, they also have a strong visual identity in the same way that ships do, so I'm not sure what your complaint is there. I can agree that infantry can be hard to distinguish, especially on darkly lit maps. I do not try to play the game without liberal use of pausing to hover over things and seeing what is what.

For rebels, if you don't use infiltrators and don't worry about unique build options from planets and ships, there are only 10 types of infantry. Once I have access to all of the tiers, I mostly just build:

--Army support platoons (medics)
--Army trooper platoons
--SpecForce Pathfinders (snipers)
--SpecForce Vanguards (missileers)

This is enough to deal with almost any threat and be pretty efficient. So if you are trying to avoid variety, I would say that is your infantry roster (I mostly just go heavy on the tier three options, tier 2 is only a small number). I will add a few support vehicles as needed (T1-B for AA, MLC Artillery, AA1-C for crowd control). That is really all you need to be able to deal with pretty much everything. Add heroes for best results.

Of course, there are lots of different ways to play and the other factions have different rosters. I would just say that most units have a purpose and the ground strategy is neither simple nor boring. You need to understand what your units are good at destroying and which units are a threat to them.