The DSP is a leftover from when there was only 1 SH-2. It was designed to help there. But with the second SH-2 it becomes a bit pointless. It still has some tasks it can do, but there very specific and you have to really think about it before hand to build your engine around working with it to avoid stalls and bus contention.
Removing the 2nd SH-2 though isn't really better here though as the Saturn is significantly weaker with out it. Early games like Panzer Dragoon, Virtua Fighter, etc. are examples of probably the best you could expect from a 1 SH-2 design using the DSP to help. Those games are only using 1 SH-2 because the 2nd one was added late in development and they didn't have time to go back in and rework the game to use it.
Personally what changes I would make would be the following:
- Combine HWRAM and LWRAM into 1 unified 2MB bank using the same memory type as HWRAM. The 2 1MB banks are a cost saving measure and and LWRAM is slower than HWRAM.
- Add UV Texture mapping support to VDP1
- Add a 256/512 Pixel Wide mode to allow for more flexibility and color options.
- Allow VDP1 to use additive blending for transparencies.
- Fix the pixel overdraw issue with VDP1 so transparencies are actually useful.
- Make VDP1 faster.
- Add ADPCM support to the SCSP.
- Double VDP1 and VDP2's VRAM.
Those aren't too much of a radical departure and they're things that would be realistic changes Sega could have made if they say decided to delay Saturn for a year to refine it and do a global Launch in late 1995. Honestly though I'd say without hardware changes the Saturn could have still fared better had Sega just not completely fucked up the Launch. That launch made the system look really weak and bad and it never really shook it off.