That's the thing though: Noctua was early (if not first) with many of what are today standard designs, and they helped move heatpipe-based CPU coolers towards their functional peak. The problem is that once these design conventions are established and in use, they are easily copied and iterated upon, and due to the limitations of phyics there isn't much to improve upon that meaningfully improves thermals. Fans are a bit of the same, though given that fluid dynamics is a lot more complicated than heatpipe-assisted thermal transfer from a source/cold plate to a fin stack, there is more room for differentiation there. That's also the "problem" you point out - there really isn't much differentiation possible when it comes to heatsinks. Soldered or unsoldered pipe-to-fin connections; soldered or pasted bases; aluminium, copper or direct-touch cold plates; infinite minor variations of fin shape, density and layout that ultimately don't vary all that much beyond the main factors of surface area and thermal mass and thus leading to hundreds of heatsinks across the spectrum of possible sizes and shapes, etc. - and thermals (with equally performant fans) being in line with this. That's just physics.
But you point out one important thing: most of Noctua's current designs are quite old. The NF-A12x25 (and to some extent the NF-A12x15) are their only recent fan designs - the rest are nearing a decade old at this point. The same goes for their heatsinks. And Noctua are infamous for slow (and constantly extended) development cycles - the A12x25 was delayed by ... two years, I think? The cromax version of it has been delayed at least twice, as has the 140mm version. This is definitely a point of criticism - letting perfection be the enemy of the good, and all that. This also lets competitors catch up in many ways. Still, it will be really interesting to see how their 140mm design pans out when it arrives (at some point), as there are few
good 140mm fans out there (but plenty of okay/decent ones).
Is the argument for Noctua's premium-ness today weaker than five years ago? Obviously, at least for heatsinks. Their fans are still top tier, but heatpipe-based heatsinks are a commodity by now. As for fans, given that they're still mostly relying on older designs that several competitors have caught up to, that is also a weaker point, but their new designs show that they still have something to deliver here. That doesn't take away from other innovative actors in the same space, but neither does it show that Noctua's premium is entirely undeserved. What it does show is that those able to deliver nearly the same at much lower cost and complexity (looking at Arctic once again) deserve even more recognition for doing so.
Also, I don't know where you're taking your dBA or CFM numbers from, but it's important to remember that there are no widely accepted industry standard ways of measuring either, so spec sheet numbers are generally not comparable outside of the same company. If anything, the wide range of well-performing heatsinks with different fans out there shows that these numbers alone are a weak benchmark as well, as they don't tell us anything meaningful about the specific airflow patterns of a specific fan design or how it interacts with the specific mounting and fin/pipe layout of a specific heatsink, etc. Things get complicated fast once you start mixing several variables like that.
When it comes to pricing though ... I definitely prefer buying Arctic P-series fans at €8-10/fan vs. Noctuas at €20-25/fan, but then I would much rather pay €20-25/fan for quiet, well-performing Noctuas (or the new Phanteks ones, if they fit my case) than similarly priced RGB-laden, noisy and poorly performing fans from all kinds of brands at the same price (Corsair, EK to some extent, and heaps and heaps of others). As such, I see no reason to single out Noctua as particularly poor value - but then I don't see fan RGB as a big value add. Other people have other priorities, which is obviously entirely fine - and they can just buy Arctic's RGB fans instead
