Dos 6.22 and Win3.11.
Much more usable than I remembered. Was kinda sorta able to get online with a PCMCIA Ethernet card.
Aside from the whole, well... lack of HTTPS support in any browser you could possibly use on that OS. Also in Win95. And Win98. But regardless...
The UI was very straightforward even then. Open folder. Click icon to run app. It wasn't hard to use. Like you say, the bigger issue was the amount of power we had under the hood. Task switching wasn't perfect but it didn't exactly hurt us then, either.
I realised that for as long as I have had a Windows system (all the way up through to my Win10 box though I now prefer xUbuntu)... I always did something that is kind of a holdover from my days of using Win3.0... Instead of using the start menu, I put shortcuts to all of my mostl commonly used apps in a folder called 'Proggy Bin' on the desktop so I can alt-tab to it when I needed to instead of dragging my mouse to the corner. So, in some ways, the old Win3.x UI was more productive in my workflow.