I think that’s true for most of us. Tanks are the larger investment so it makes sense to zone in on those units. Most mainline infantry is fairly replaceable outside of fully vetted Rifleman with double upgrades
Imo max vet mainline are as good as stock elite, so they should be treated as such. However, some infantry benefit more from vet.
in terms of heavy, I think most heavies are in a good spot, while others just in need a little bit more tinkering. The balance team made a series of changes that brought heavies from a bad unit that, was only good for rushing, to OP unit with timing and then brought it again to a decent unit. Although, most heavies are not as efficient as mediums. They do reduce the burden of micro by a huge margin. It is still a gamble tho, kind of like with the famous proverb of putting all eggs in one basket.