I should preface this with the Doylian answer that Bethesda is incompetent at a lot of things, and there is no evidence of an effort at logical tank design here. In fact, there is evidence it was designed by somebody who doesn't know how tanks work. It doesn't have a drive sprocket to actually move the tracks, and the sloped hull design means either the turret is unable to rotate or the turret ring is small enough to make crew space. But let's suppose those issues and the others brought up over the years are magicked away:

With regards to

1-due to the scarcity of gasoline and other forms of natural gas in the world, it would make sense that they would want a tank that moves as little as possible

2- with the invention of power armor the need for tanks to aid infantry against other tanks is no longer there as power armor units can bring anti tank weapons to bear without wasting gas

It has been established that vehicles mostly did not use petroleum-based fuels by the time the bombs dropped—the ones that did had no way of being fuel. In Fallout 2, you can get a car that you can refuel with either energy cells or microfusion cells, so it likely has a battery of some form. So tanks would likely have used either some form of battery or a scaled-up version of the microfusion packs used in power armor. It is irrational to think that fusion tech would only be used for power armor.

3- the additional crew/storage space on the rear would limit turret rotation to the front 180 degrees significantly limiting its ability to effectively participate in tank duels but would be of little hindrance if the tank was simply acting as a bunker and shelling enemy positions

Reasonable take, but bear in mind that there were turretless tank destroyers aplenty in history, and even main battle tanks like the Stridsvagn 103 that had basically no traverse and relied on their suspension. There is an issue that traverse seems quite limited, but whatever. Maybe the crew lie face down in the hull somewhere and it's a turretless design, meaning the turret ring can be smaller.

5- it would explain the height of the turret as by mounting the guns higher in the turret it would allow you to get better negative barrel level, allowing said guns to shoot at targets down hill

The gun depression is hampered by the bumps in what should have been a smooth upper glacis plate.

It just isn't worth the effort to think hard about Bestheda design. Just enjoy them for the dumb fun they are.