This is false, the 76 has a higher firerate than the 85 thus making it stronger vs infantry, for a difference of 40 fuel. If you want to look at an actual upgrade compare SVTs to 7 men for instance, svts bring way higher dmg output and you can get them way earlier (cp1) compared to tier 4, literally a better option in every way possible while 76s are not too uncommonly a better pick than an 85.
A slightly faster rof vs more armour, health and pen and iirc better aoe profile. Totally not a direct upgrade, not like the "instead of a more durable squad with cheaper models you shoot more"
7man and svt are like 5th man and lmg for grens. It's not an upgrade over one another its a divergent path. 85mm t34 is an upgrade over the 76mm in the very literally sense.