Turned out the sane web interfaces were as horrid and frustrating as the other ones, so there is nothing left to do but to either build a working front end or use the scanner in a sub optimal way that will certainly result in the machine being dumped in the attic at some point.
Now, what do I want when interfacing with a scanner on a mac? Do I want the same scanner interface I have seen since the first flatbed scanners I owned in the 90's? Those massive windows with a thousand options? No! The reason scanner software worked like that back then was because processing speed and storage where a thing. If you did not need to scan 1200DPI full A4 full colour uncompressed, then you tried to avoid it. Made sense then. Not now. Even with USB2 speeds and a moderately capable network, the loads are negligible.
It is perfectly reasonable in 2020 to simply request the entire page on any resolution and crop it afterwards. It is just as quick and far more convenient.
So, on a mac, what would be the ideal way to use a flatbed scanner? A simply short list of options that result in either a text or an image document opened in a suitable application. Basically I want to quickly command the scanner to scan 300DPI in greyscale and open it in preview where I can crop and save. That is all you really need for 99% of the time.