My thoughts on this are as follows:
1. If you compare what you get from the $7000 base model 2023 Mac Pro and what you got from the $6000 base model 2019 Mac Pro, the former is a way better value. You were never going to get anywhere near 24 Xeon W cores, 64GB of RAM, and anything even remotely as powerful as even the 60-core GPU that the base model M2 Ultra has for $7000 on the 2019 model. Not to mention the base SSD capacity is doubled (though, for Apple's rates, you'd hope so).
2. However, if you compare the $7000 base model 2023 Mac Pro and the $4000 base model M2 Ultra Mac Studio, the former is an extremely poor value. Two extra fans, two extra thunderbolt ports, one extra 10GbE Ethernet port, internal USB-A and SATA ports, and PCIe expansion is not worth $3000. That's really not how the computer industry works.
3. Apple was never going to have memory expansion separate from the SoC choice. However, not having the SoC be socketed was a poor choice for a machine the primary purpose of which is unfettered aftermarket internal expansion.
4. If Apple's claims that the M2 Ultra is more powerful than the 28-core Xeon W that one could max out a 2019 Mac Pro with are true, then the lack of CPU options isn't terrible. You have one choice and that choice bests every 2019 Mac Pro CPU option. What more do you need on the CPU front?
5. If the M2 Ultra with 76 GPU Cores beats out the best MPX AMD GPU combination that you could stuff in a Mac Pro, then that's one thing. However, I'd imagine that there are some workloads where you want multiple GPUs; one to do your rendering, and one to display the system's output. If software sees this as two M2 Max GPUs and will allow for that kind of split-task workloads, cool. If the 76 (let alone 60) GPU core option does this and beats out the best that you could've stuffed into a 2019 Mac Pro in terms of MPX modules (Dual W6800X Duos?), even better. I'm guessing it can't. But if it can, then my "what more do you need?" question stands for GPU power too. All of that sounds pretty iffy so far. But I'll reserve judgement until people get their hands on 2023 Mac Pros.
6. A maximum of 192GB of RAM is one fourth the 8, 12, and 16 core 2019 Mac Pro's maximum RAM capacity and one eighth that of the 24 and 28 core models. While, 192GB is a staggering amount of RAM, I can't imagine that there weren't 2019 Mac Pro customers that needed 256GB or more. Yes, unified memory is more efficient memory. But RAM is still RAM. I could totally buy that an M2 Ultra will beat out a Xeon for CPU performance and most of the AMD configuration options in play from 2019 all the way until this week. But, I'm not buying the notion that 192GB of RAM will suffice for those that needed 256GB of RAM, let alone 768GB of RAM, let alone 1.5TB of RAM. I can buy that the 2023 model is superior in performance to the 2019 model in every way. But unless the use case is fine with 64-192GB of RAM, this is the one area where this machine is a clear downgrade.
7. A fully maxed out 2023 Mac Pro is a Tesla Model 3's worth cheaper than a fully maxed out 2019 Mac Pro. Sure, most of that is Afterburner, Xeons, and Radeons and a lack of RAM options. But still. That's something.
8. The SSD kits for 2019 Mac Pros and the SSD kits for the 2023 Mac Pros are different. This makes sense. Though, it seems ridiculous that the SSD kits for the 2023 Mac Pros can't be used with the 2023 (or 2022) Mac Studio, just as it's ridiculous that the SSD kits for the 2019 Mac Pros can't work for the iMac Pro (or higher capacity 2020 27" iMacs, for that matter). Then again, I've never been a fan of this whole "SSD controller lives on the SoC" convention that Apple has moved the Macintosh to.
9. It seems like PCIe expansion is the real reason to buy a 2023 Mac Pro over a 2023 (M2 Ultra) Mac Studio. There may be other reasons to, but I can't imagine any of them are worth the extra $3000. The Rack Mountable option seems like it would serve well in a datacenter rack or in an audio cabinet. Though, for $3000, I'm sure one can find a rack-able solution that accommodates a Mac Studio that still leaves most of that left over.
10. It's totally possible that an "Extreme" chip or (other higher-tier Mac Pro chip that plugs the gaps between features the highest end 2019 Mac Pros had and what the highest end 2023 Mac Pro) has could still materialize. Apple kept adding GPU options to the 2019 Mac Pro throughout its four year reign. Incidentally, they might wait until the M3 generation to add that. Or it might just be that a future Ultra SoC will get there and that, this one just happens to be a downgrade for those that need higher-end options. I'm not saying I'm hopeful of this. But there's no reason why it can't happen.
11. Regardless of how small customer base is, Apple has no reason not to (a) keep the Mac Pro as up to date as the Mx Ultra Mac Studio and (b) introduce updates more frequently than once every 4-6 years.