Yes it would, in fact. Assume the Maus is at 7.0 as I am proposing. It has a 232mm turret face. Even with rebuffs, APCR would struggle to penetrate heavily-angled armor, because that is in fact realistic. But the “shell shattered” crap is not.
Properly-modeled 76mm M93 on the Jumbo 76, T20, or someone’s uptiered M4A3 76 would penetrate 248-260mm, which is enough to pen a Maus at close range, and easily enough to pen its side from quite a distance.
Properly modelled 76mm 17pdr APDS on the Centurions and Black Prince would pen 270mm and actually spall well unlike now. This would go through the turret easily and the sides laughably so.
Properly modeled 76mm M319 APCR and 76mm M331A2 APDS would pen 300-320mm, while spalling very well once they pen. Again, these would laugh at a Maus unless it angles all the time.
Properly modeled 90mm M304 APCR would pen 320mm, and spall more than the 76mm M93.
Properly modeled 90mm T44 on the Super Pershing would utterly laugh at a Maus with 373mm penetration.
Properly modeled postwar M332 and M332A1 APCR would cease to be fair against a Maus even with angling, penetrating 390mm and 425mm respectively.
Properly modeled 105mm T29E3 would pen 381mm, and spall more so.
The T34 already doesn’t even need APCR, but its properly-modeled APCR would pen 450mm and spall magnificently.
Russia has no good APCR rounds to speak of, but properly modeling those would turn the postwar 85mm BR-367 and the T-34/57’1943’s 57mm BR-271P into very competent ammunition to kill a Maus at least through the sides if the need arose.
And in the odd mirror matches, German APCR if properly modeled would also be capable of killing it. Long 88 would get 305mm, the fake 105mm on the KT105 would get nearly 400mm, and the Panther 75mm would get 270mm or so.
Don’t waste your time with him, trust me.