I understand that it might not be used often (at all?) during the WWII but it's not about deleting the Pershing and adding the Super Pershing. All I am suggesting is giving it an HP pool boost. It does not necessarily have to be a Super Pershing in the end. I suggested it as it is a similar vehicle with only a few changes and would be a good source for graphical model, but outside of that, I do not want to change the vehicle. If we can add a buff to the original Pershing without making it a "Super" variant - I am fine with that.
Try to compare the stats of tiger and pershing. The only important thing that tiger is better at is the hp pool, while pershing gets all the other benefits - it has higher penetration, better AI, speed and acceleration. Plus, it has totally amazing special attack and crew nades. Hp is its only disadvantage (for the record it also has lower rear armour but its not important for such a fast tank). Just learn to use tanks strenghts and don't let enemy use its weaknesses and all will be well.
You can also look at it the other way: USF has 2 amazing tanks at last tier - sherman which is great flanker and best AI med in game, and jackson - a TD that has great view range and deals with even heaviest of german tanks. These two tanks are enough to win any late game match but they have one problem - they are micro intensive and when the numbers become bigger and bigger, you need a lot of skill to manage all of them.
That is when pershing comes in - a heavy that is kind of micro intensive for a heavy as well, but still much, much less than two additional mediums. It also has good armour, usefull abilities and does the job of both jackson and sherman - being better at both roles. That's why it is needed and why you should build it. If you find pershing usefull, just like I do, and you would buy it instead of two additional jacksons, then its in perfect spot - it adds combat ability to your army while not being one tank army itself.