And to be honest, the whole concept of a Mac Pro goes against the design philosophy of Apple Silicon. The whole point of those chips is to maximize efficiency by having everything on-die or very close to the chip. For example, the M2 Max has like eight memory channels in a laptop - you could not do that even with CAMM[1] modules.
A desktop machine without replaceable RAM or slots that can accommodate GPUs is going to be a nonstarter no matter how good the the SoC's integrated accelerators are. A significant chunk of the cost of the Mac Pro is just the fancy desktop case, specifically designed to accommodate lots of expansion cards and compute accelerators. If you don't care about slots, you can just buy a Mac Studio for less money than the Pro. If you do want slots, only being able to plug in storage and I/O devices and nothing else is going to be a huge drag.
[0] Apple Silicon PCIe controllers have a unique limitation in that they prohibit accessing external memory devices. This is why Thunderbolt eGPUs don't work - the M1 and M2 can't actually write to the memory on the GPUs.
[1] Compression Attached Memory Module, a JEDEC standard for a thin dual-channel RAM card promoted by Dell to allow socketed high-performance RAM on business laptops.