Thanks for the feedback.
Before switching to watercooling, my go-to brand for ventirads was Noctua indeed. Never used Be Quiet so far, but I've only heard good things about them.
Just to reply to the point of watercooling failures: I haven't had that many over the years: essentially one bad failure, a leak in some Corsair AIO (so not your random cheapass shit) which ruined a graphics card. And then as I said, occasional annoying air bubbles and pumps sometimes failing to start. Yes, most watercooling pumps are pretty finicky due to their simple design, and sometimes the tiniest air bubble may make them fail to even start.
But as I said, it's also just the maintenance factor and the objective fact that watercooling has more probability of failing than just a ventirad. Having to flush it every year or every two years is not a huge deal but it's annoying. And moving a computer with watercooling installed is always tricky.
And yes, a fan failing on a ventirad (and I've personally never had any fan fail) is less serious usually. You have significant leeway and enough time to act before it gets too hot, while with watercooling, if the pump fails to start, it just gets to > 90°C temperatures within... seconds. Pretty bad.
Problem with those bulky ventirads is that many of them are very hard to fit unless you use the restricted number of motherboards listed 100% compatible. If not, most of the time, they just get too close to RAM sticks or even prevent to install them altogether. Major pain. Another point I'm not very comfortable with is their weight. Must put some nasty constraint on the motherboard, however sturdy the backplate is, especially when in a vertical tower.
I mentioned the Dark Rock 4, I've seen tests which show just about 3° above what you get with the Dark Rock Pro 4 (which is the bigger one and closer to the Noctua ones mentioned here too), but it's significantly smaller. So that may be adequate. Would be cool if anyone here had experience with it.
I've also seen the relatively new Deepcool AK620, which, while "cheap", seems to be one of the best at the moment from tests I've seen. But it is also big and heavy.
Also wondering if anyone else had or was having the same thought as me, going back from watercooling to aircooling, to hear about their experience.
I might also end up sticking to watercooling, who knows. Possibly using better pumps and a reservoir easier to flush would make things a little less annoying.