One does not get the 76mm for fighting infantry, they have 75mm for that, but for fighting vehicles.
76mm is quite good at fighting vehicles with it penetration/accuracy values are above other tanks of its class.
You clearly not getting 76mm for fighting vehicles but for beeing a generalist tank that can fight vehicles and infantry alike. For fighting vehicles/tanks both faction with 76mm have a clearly better nondoc alternative in M36/SU-85 which come in the same tech. 76mm (and E8 too) are only worth it if they don't fall too far behind nondoctrinal options in AT
and AI.
At Land Lease it has to compete with combo of T34/76 for AI and SU-85 for AT. While I can see its use in AT because it has some advantages over Su-85 (primarly its turret and mobility) its AI performance is way worse in comparison with T34/76. This is the reason Soviet players will choose T34/85 if they want a doctrinal generalist tank option. T34/85 has the same AI as T34/76 plus some more advantages over Su-85 (primarily turret, mobility and survivability).
At Mechanized 76mm has to compete with the nondoc combo of M4A3 HE shells for AI and M36 for AT. With the double nerf to RoF its AI value got hampered so much that it is falls far behind AI value of M4A3. In addition there is not really any advantage over M36 which is quite mobile and turreted by itself. That is the main problem of 76mm and E8 too by the way.
You are locking out indirect fire options, elite infantry like Paras or Rangers by going for 76mm or E8. As long as this two tanks are no real alternative for nondoc tank combos this companies won't be competetive.
Imo both tanks need an AOE buff as I already suggested.