No, I don't think I will give it time. UIs should nearly never be changed. It doesn't matter much whether or not it's an improvement. Don't monkey with other people's tools.
I've said this before, but it's worth saying again:
Define "improvement".
Because the best UI (as in unquestionably the absolute best) is the UI that you're already an expert with.
Can there be better UIs later? Yes.
Can there be better UIs for new customers? Yes.
Can there be a better UI than the one you're already an expert in? NO! At least not until you do the work to become an expert in the new UI all over again.
At a minimum, you're asking users to trust you that re-learning their UI will ultimately be a better experience for them. Because it will absolutely suck for your existing user base when it first changes (this is why UI changes are almost exclusively met with negative backlash from the current users).
Can you do that? Sure. Do companies do it often? Nope. The vast majority of the time, the UI is changing for one of two reasons:
1. The company believes the new user experience is better with a different UI. They are actively trading existing customer satisfaction to improve metrics around new users.
2. The company believes they can drive users to new features with a new UI. They are actively trading existing customer satisfaction to improve metrics around new features.
Neither of those are compelling reasons for a new UI from the perspective of an existing customer.
Broadly - they might still be an acceptable trade for a company on the whole. But don't expect happiness from your current users, and be very wary of the churn and brand loyalty you're burning by making the change.
Don't believe that was worth saying twice quite frankly you're the only one trying to redefine "improvement".
Here's a very simple non-UI example for you. You have learned to cut an onion one way. It takes 5 minutes to cut it that way. Someone else comes along and tells you that you can cut it this other way, and now the process only takes 30 seconds. Is there some learning here? Yes. Are you suddenly incapable of cutting onions or are no longer an expert in cooking just because you learned a faster way? Absolutely not. But overall it is an improvement including any learning process.
Existing customers who remain stagnant because they are terrified of any change are customers who eventually leave when they're marketed to by someone else. It's truly that simple.
Don't get it wrong, this isn't an argument in favor of mindless UI changes (and frankly Thunderbird's changes are garbage) as bad UI updates do exist and should be argued against, but this idea that improvement doesn't matter is so beyond absurd!
So Windows 1.0 was a "modern", "clean" (i.e. flat) user interface, like Windows 10. They have a substantially different color scheme and a substantially different layout preference, but we can pass them off as theming and pretend this matches.
It had a panel at the bottom of the screen (showing background apps) and tiling windows for non-backgrounded apps. Windows 10, by comparison, prefers you to run maximised apps and has a panel showing all apps, including some that haven't been launched. Despite the fact that a user experience for Windows 1.0 and Windows 10 could be roughly the same, the Windows 10 user is not required to maximise their window and can have multiple, user-managed windows. This is vaguely similar, but I think the dissimilarities are starker than the similarities. Especially since the panel explicitly draws inspiration from other operating environments - if it is similar, it is because of a common language rather than because of heritage.
Windows 1.0 made use of menubars to hide their functions or to make them available. In Windows 10, the menubar is essentially deprecated - it still exists, but most Microsoft/inbuilt apps use ribbons or hierarchical page-style apps (I don't know what to call them - apps whose UI draws more on mobile apps than the desktop tradition).
Windows 1.0 exposed your computer to you in terms of the file system, kinda like the Mac did. Your prime UX helper was the MS-DOS Executive, which was the predecessor of File Manager/Windows Explorer. By Windows 3.0, this system was essentially abandoned and applications were presented separately from the filesystem, first via the Program Manager and then by the Start menu, eventually adding the taskbar/panel into the mix. This system remains to this day. I think this is a massive difference, it is insurmountable. The idea that the filesystem is a scary interface means that your operating system mediates between you and the stuff on your system, rather than being a tool for accessing it. Your C: drive becomes Windows' private database that it uses to store your programs and data - effectively a local cloud, making the transition from "your computer, your files" to "Microsoft's computer" obvious. It was clearly no great conspiracy - Gnome and KDE and XFCE, to say nothing of all mobile phones, do the same thing; it was a natural evolution in making computers easier and safer to use. But the ramifications of the change are significant, and the implications for a comparison of Windows 1.0 and Windows 10 are significant. However, I think you're mostly comparing Windows 1.0 to Windows 10 in comparison with Windows 1.0 and perhaps Windows 2000, and in this regard, yeah, sure, maybe we have to "price in" this change.
Windows 1.0 made very limited use of graphics and animation. Windows 10 pretty much is scared that you're illiterate (fair enough maybe, we can process graphics pretty quickly compared to text). It's certainly worried that you might have an attention span, and does everything it humanly can to prevent that. I think the difference between Windows 1.0 as a "good faith" tool and a work in progress, versus Windows 10 as a deliberately distracting entertainment device, designed to prevent you from doing what you want today, is also a massive change. Understating it does us a massive disservice.