I'm not entirely sure about it. The shell switch delay does make the switching of shell in the middle of a combat pretty much useless. So if we assume we have two of them and are fighting a mixed force 2x 76mm would be still worse than a M4A3/M36 combo. Why? While one 76mm would be just a more expensive copy of M4A3 with HE shell which can do nothing versus tanks, the other one would still underperform in AT comparison to M36 with an AP shell that does nothing versus infantry.
The bonus in variety would be using both with HE or AP shell if you are fighting infantry or tanks only of course. Still you would have your pants down if you run into the other kind of unit type. In addition the 76mm doesn't scale very well versus the late game tanks. I do think it wouldn't be broken. And if it turns out to be too good after all you could just balance by delaying the shell switch further or adapting unit cost.
Either way HE/AP shell switch could work out because 76mm would be a straight upgrade of M4A3 instead of beeing inferior to M4A3/M36 at AI and AT.
Yes it would be OP, having a single vehicle with the best HE round and the Best AP round is simply too much. Changing shell is close to simple reload so it less of an issue than it presented.
76mm/M36 combo would better than M4A3/M36 because it would have same AI and far better AT.
The 76mm scale better than other mediums versus "late game tanks" when in numbers it can take many of the "late game tanks".
The M4A3 is one of the most cost efficient stock medium tanks and m36 is OP by design, trying to create a unit that outperform them is simply asking for trouble.
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cblanco ★ 
Heartless Jäger 
