Didn't you sort of answer your question yourself?
I used to think biggest is best was a no brainer in armored vehicle design, until I ran into logistics issues too. Now I'm experimenting with how light I can get away with, and have APCs that do no require much more fuel than trucks (which I have yet to field and try out for good).
It all depends on how much fuel you can produce, and how much you can move. Early game, when logistics is all trucks, I'll try and stay cheap, but later when rail is used to move the bulk of the supplies from the SHQ to the city closest to the front, whose truck station is only dedicated to bring them to the troops, I might go with heavier, fuel expensive vehicles.
It also depends on who you're facing with: minors and independents are much easier nuts to crack than majors equipped with advanced techs. I like my armor to be at least as protected as my enemy's infantry.
But if after I run a whole mechanized brigade 100 Action Points forward I need to park units along the road for two turns to protect the supply line while the fuel tanks are replenished, I decide I should have gone more on the affordable side of the curve.
And as Culthrasa said, technology is important too. For example, polymer armour is lighter than steel for the same amount of protection.
< Message edited by Jdane -- 7/17/2020 10:10:03 AM >