I used to believe the same thing, but that's just Apple propaganda, pretending their stuff is better than everything else when in practice it's not always the case.

It would be an argument if Mac native development could be ported to other platforms relatively easily. But that would take Apple to care about anything else than itself so it will never happen. As is, it only makes sense to develop a Mac native app if you are absolutely sure that it is the only platform you want to target.
For this reason, there are some successful niche apps, but I believe that it is not a very good idea for the vast majority of projects.

Apple has some good librairies that can speed up the dev process of some specialty apps, but if it becomes a complex long running project, it is most likely going to bite you; because of being tied to the Apple agenda and the fact that they have zero problem in deprecating everything every 5 years or so, creating much unnecessary work and erasing a lot of value creation.

And this is under the assumption that Apple native stuff is inherently better than other native stuff. That used to be true in some cases, but with recent developments I don't think the argument holds up. Native stuff does not bring a lot of advantages while not feeling much faster than alternatives and recently being even more bugged than you would expect. Anything swift is generally just not very good when it's not just plain bad. I think the native Reminder app just got barely usable, after like 3-4 years. At this point I prefer electron stuff...

The argument about ressources and bloat is typical Mac user stuff. It only matters because Apple is a greedy corp charging way too much for way too little. People using Mac have to care, because there is a very real and large cost to overprovisioning your system to guarantee performance.
But the reality is that RAM is cheap and storage is even cheaper (especially if you don't need to have the fastest thing around) so it doesn't matter. People who want/need fast system in all conditions just max out their RAM to 32/64GB and their SSD to multiple of terabytes. It cost them less money than it cost upgrading 8GB of RAM at Apple.
And while every Apple fanboy is boasting about Apple Silicon battery thanks to its power consumption the reality is that you will find computers that cost half to 2/3 of the price of Apple's cheapest offering that perform at least as well (from a benchmark standpoint) but in practice much better in real-world use (because of many factors, like application technology just like this post says).

Alos, on Windows 11 WhatsApp uses 50-80MB of RAM but that's not surprising considering how bad macOS is with third-party technologies. In general, there is some widely held belief that macOS (and Apple stuff in general) makes better use of the hardware. As someone who runs both systems concurrently (and even ran 2 identical Mac Minis, one on windows, on on macOS) I can say that this is a load of horseshit.
I find Windows to be less ressources intensive, especially if you have a dedicated GPUs, then system RAM use is much lower. A major problem the Macs always had was poor GPU specs, but they made it even worse with Apple Silicon, because, surprise, you need to share your overpriced soldered memory just to display stuff too.
Isn't it nice? This was an intended consequence and the unnecessary RAM soldering (somehow justifying the absurd price) just a means to an end: make more money, with absurd margins.