1. Obviously having to switch between two shell modes to get good AI or good AT is a disadvantage compared to a tank who has the same AI and AT values combined in one standard shell. I do think this is out of question.
2. With the nerf to RoF AI and AT performance of the standard shell the 76mm got worse at AI and AT compared to the performance it had before. This one should be out of question too.
3. Given the armor values of axis tanks 120 long range pentration with a RoF above 5 seconds shouldn't be considered as "good at AT".
4. A 80 damage kill radius of 0,88 in combination with an AOE of 2 with a far damage of 8 shouldn't be considered as "good at AI". It is in fact the worst AOE profile of all generalist medium tanks (shared only with E8 shells and AP shells of 75mm Sherman).
The idea of a shell switch is that you have a strong AT shell with little to no AI value and vice versa. both shells should be individually stronger in their section than the shell of a similar priced tank which combines AI and AT in one shell. This mechanic should be obvious to all around here.
If a tank fails to be good in one of the two shell modes the shell switch gets obsolete, because you will be pretty much always be in the other better mode.
While HVAP shell of 76mm is good at AT, standard shells are not good at AI and not good at AT either of course (see 3. and 4.).
With 76mm standard shells not beeing good enough at AI and HVAP easily getting overshaded by SU-85 in range, accuracy, penetration and RoF there is no reason for the existence of M4C at a Soviet commander.
I'm done.
What you are describing is the ISU-152 shell that AI or AT (and even that is not very accurate since the AI shell have deflection damage) and not the Sherman shells.
The 76mm AP rounds are simply not bad in AT. Here is a simply DPS comparison between the 76mm and Ostheer PzIV in live.
PzIV vs Sherman 76mm has 21.7/19.2/15.8/12.8/10.0 DPS
Sherman 76mm AP vs PzIV has 27.4/23.1/19.0/15.3/11.7 DPS
as you can see 76mm is higher DPS at all ranges so the AP rounds are good at AT.
As for its AI it probably the same to the 75mm AP rounds only it has higher ROF.
If you want more accurate stats you can ask Hannibal to provide you with the AT stats and MMX to provide you with AI capabilities of the 76mm Sherman.
76mm Sherman can use AP round and if it engages a vehicle with high armor it can easily switch to HAVP after firing the first shot and during reload and use HAVP that is simply not a disadvantage.