So, just to give a status update since I started this thread.
I’ve browsed through reviews for the mentioned Brother All-in-one on Amazon. It seems to have huge problems with connectivity over WLAN. Would not wake up, loose connection in the middle of a print job and so on. Judged by the time of review, it is not fixed in 2018. Seem to be a difficult job for Brother, only that people manage to sqeeze WLAN in watches these days. Buying myself a load of trouble for 300 € is not a good idea, so I’ve decided to look around.
HP: Overpriced, deliver their printers with 600x600 resolution. Seriously? In 2018? My HP LaserJet in 2000 had the same resolution. Time seems to stop at HP Headquarters.
Samsung: Seem to be descent printers, but people complain about not having drivers for a recent version of macOS and support being handled by HP, at least here in Europe. Looks to me like their print division is on the edge of being sold.
By this time, I backed off from the Idea of buying an All-in-One since no satisfying offers exist. My idea was to go for a simple black&white printer again - with wlan support and duplex. Even this is very difficult. Small b&w printers these days seem to be as crappy as inkjet printers. They are expensive for what they do (mostly over 100 €), they have expensive cartridges (mostly with chips, to stop you buying from third-party vendors) and page counter in cartrigdes. Resolution is bad, memory is scarce, which is critical for a network printer. Models from 2014 had at least 64 mb, models from 2017 have only 32. It really seems that consumer printers go back in time and are getting crappier and crappier with every year.
So I made a roll again and went for a small office color-laser: Kyocera Ecosys P5021cdw I was able to get it pretty cheap on amazon (160 €), It can be used with third-party cartridges, which is a huge plus, has wlan, duplex and honest 1200x1200 dpi. Color print is a welcome plus, but it can be switched to a black cartridge usage only, so color cartridges are not used. At this point it should get very cheap.
Summary: Oatmeal is right: printer industry is full of crap and is getting more and more worse. They all have some problems, they can’t solve simple technical problems like connectivity, they break easily, and so on. The only field where they show some creativity is by trying to rip you off with cartridges. And I am not talking about very cheap printers - I’ve inspected devices in the range of 100-300 €. If you can, go for office printers - they are built for last and have lower costs of service.