What if I actually told you that both 88mm and 75mm had higher velocity and joule rating than is2 main gun, thus they were historically better ?
And if out of all three guns 75mm was better than both ?
The idea that 122mm is better than 75mm because more is totally wrong, caliber is not the only important feature...
This is wrong and a often repeated myth.
1. Tanks fought infantry and emplacements more often than tanks in WW2, so higher caliber = better since it deals more damage.
2. The 122mm gun of the IS2 could penetrate slightly more mm of steel than the Panther.
3. The gun of the IS2 and also the kwk 36 8.8 of the tiger could penetrate any regular tank with ease despite less velocity than the 7.6cm of the Panther. So in most situations higher caliber = more damage = better.