It is nice when people try to think in new ways, but do they have to try to ram it down our throats?
It looks like they did not even bother to test it on large monitors…
(It is this post: https://eskerahn.dk/?p=23 , note the side by side images )
Sure for those still designing pages to be primarily used on 640×480 VGA screens, this short of 600 pixel width could make some sense – but for us not on windows 3.1 any more, well VGA is not the target platform…. 
Why not check the THEME the user got installed for the page, and adjust the width according to this? That does not seem like an extreme idea, if you claim that you try to give users an editing experience closer to the actual result…. 🙄
What about this totally messed up old table:
(From this ancient post: https://eskerahn.dk/?p=6 )
Frankly I do not even bother to see if this new system has any benefits, when basic stuff like this does not work.
And anyway, why not start a load after upgrade with a splash screen like “We offer you a new editor experience …blah blah… Try it out”, and then have it as an OPTION!
It is grotesque that we explicitly needs to INSTALL a functioning editor! 😯
So thank Gods for the offered plugin “Disable Block Editor“, thank you Mr Milan Dinić , I hope he gets rich by a few millions others than me paying him a few dollars!!