"I wonder how many people really need all the power of an M3 Ultra or whatever versus people just liking the idea of a large performance headroom" is a reasonable query. My response (other than the obvious YMMV) is that users
A) accustomed and accepting of the substantial latency of older boxes and
B) using only one app at a time can suffice with older hardware; particularly if they also choose not to upgrade that single app.
However in my experience:
A) The reduced latency of more modern hardware has a huge impact on one's creative capabilities. When the software responds more quickly, one's brain also responds more quickly. [Note that I am not talking about silly brain-dead YouTubers' videos doing things like comparing render times 20 seconds versus 60 seconds which are not really very relevant; I am talking about milliseconds differences in real operation affecting thought processes, not feasible for clickbaiting videos.]
B) Many users multi-task and/or use multiple apps at the same time in their workflows. The additional RAM available with more current hardware (e.g. my 2016 MBP max available was 16 GB RAM while my 2023 MBP max available was 96 GB RAM) facilitates much smoother workflows. Again, when the hardware/software responds more quickly, one's brain also responds more quickly; it is synergistic.
C) Latest app versions in general tend to allow more effective real work. Latest app versions in general also tend to optimize with or even require modern hardware.
D) Latest OS versions in general tend to be more secure and add features that allow more effective real work. Latest OS versions in general also tend to optimize with or even require modern hardware.
E) This is tech. One very literally does not know what one is missing when one plods along using hardware/software a decade old.
Bottom line is yes upgrading has value. Each user decides where the cost-effective purchase lines are. Personally I have for decades found top hardware and maximum available RAM appropriate and cost effective, 5-7 year life cycle. YMMV; however all buyers need to think forward, not backward (even though most here continue to buy, esp. RAM, based on what they did last year when they are buying a box for future years; go figure).
I think you're honestly leaning a little too much into artificial benchmark results for the M-series, based upon your points A) and B) above. I am curious what your actual workflows for your setup are, because that would go a long way toward actually resolving whether the generational improvements between the M2 Ultra, M3 Max, and a future M4 Max/Ultra will actually be truly noticeable.
But comments like this "Again,
when the hardware/software responds more quickly, one's brain also responds more quickly; it is synergistic.", make me honestly question how much of this is actual product frustration versus just rage posting, and why I want to know what your workflows are exactly, to see how almost imperceivable differences in response time for normal applications, are going to have this much of an impact in your day-to-day usage.
Similarly, you make a case for "more RAM" facilitating a smoother workflow, because your 2016 MBP had 16 GB and your 2023 MBP available is 96 GB, but you're talking about a complete architectural change, significantly more cores, etc., and it's probably not the additional memory that's anywhere near the largest contributor toward your smoother workflow.
Overall, this honestly seems like a fairly disingenuous argument/response, because we're not comparing the M3 Max or a future M4 Max/Ultra to a Skylake-based MBP; we're comparing the current M3 Max against the current top-performing Apple Silicon M-based chip, the M2 Ultra. Nothing that has been presented by anyone, has made the case that the M3 Max will have any greater of a lifecycle than the M2 Ultra, and the M4 Max might not see it either, because of the shear performance of the M2 Ultra. The M4 Ultra obviously will surpass it, if Apple releases one, but we're probably talking about several months to almost a year away for its release, and I think that anyone who reasonably wants "the best performing Mac available right now", could purchase an M2 Ultra-based Mac Studio or Mac Pro (though the latter, I wouldn't probably recommend personally), and could generally ignore the "two generations behind" argument.
Now, are there instances where someone can take advantage of ray tracing, mesh shading, etc.? Absolutely. And in those instances, it could make perfect sense to go M3 Max over M2 Ultra, and to argue for greater hardware longevity based on that. But "macOS updates" and "responsiveness" isn't one of them.