There are already a lot of vehicles that have even more powerful HE at lower BR. they are not “breaking” the gameplay. let’s have a look
Sturer Emil = BR 4.3, 37mm HE with 880 m/sec and a APCBC-HE, 15 sec reload, some fromtal armour
15cm sIG 33 B Sfl = BR 1.0, 61 mm HE with 240 m/sec and a HEAT round, 11 sec reload, low profile
Lancia 3Ro = BR 1.7, 27mm HE 399 m/sec with 10 sec reload, HESH and HEAT available
Zrinyi II = BR 2.7, 27mm with HE 471 m/sec, HEAT available, 10 sec reload, good armour
KV-2 = BR 3.7, 48mm with HE 530 m/sec, SAPHE available, 33 sec reload, good armour
Brummbär = BR 4.3, 61 mm with HE 240 m/sec, great armour, 17.2 sec reload
Lorraine 155 Mle.50 = BR 4.3, 61mm with HE, 563 m/sec, 20.00 sec reload
Ro-Go Exp., BR 1.7, 25mm with HE, 580 m/sec, 10 sec reload
Ho-Ro, BR 1.3, 55 mm with HE, 290 m/sec, 14 sec reload
Spj fm/43-44, BR 1.7, 48 mm with HE, 285 m/sec, 15 sec reload
there are plenty more powerful derp guns already in the game and nearly all of them are lower BR than the T-34 and It still works and everyone is happy with it. They turn out to be so effective that nearly no one uses them with those rounds when other rounds are available. and seldom does someone bring them in the up-tier.
so I do not think there will be any issue with the T-34. in fact, the T-34 will be pretty effective against it.

