Yes, really. Why should that surprise you? The majority of XUL extensions had not been ported to WebExtensions when Mozilla pushed this update and Mozilla was well aware of that fact. This was executed poorly and Mozilla deserves to be criticized for it.
XUL extensions e.g. the user interface could not be ported, the notice they were given was "this will stop your extension working" with users being given the advice from advocates "don't worry we'll build some replacement APIs sometime soon..."
There were years of notice, but no infrastructure to support addons migrating to WebExtensions. They're still working on the supporting APIs now, after throwing the switch. What would have made more sense would be to bring in support for WebExtensions and all APIs necessary to replicate popular addons first, give them enough time to migrate, and then disable legacy extensions.
Technically yes, there is the ESR version available until April, but the vast majority of regular users aren't going to know about that.
By far the vast majority of popular extensions were ported well in advance, NoScript[1] was a notable exception, but even Tree Style Tabs is available now.
[1] I've found uBlock Origin in dynamic mode to be superior to NoScript, anyway.
TST is available, but in its default state it has tabs listed across the top and also down the side. You have to edit some other file manually in order to hide the tabs from appearing at the top. TST tells users about this but also disclaims the possibility that following the instructions to do so may break things. This is not exactly a smooth transition.
Right on, was using hide the title bar[0] add-on which gives you a script to install, and then it runs the script on window creation, but need the keymap since it comes back after every window resize. Just need to edit the extension to run on resize really, if possible.
