Doesn't that just tell you that most (web) designers aren't using IE 11, because that's the audience for webflow.com?
It's an interesting statistic, but it's not news, unfortunately, and doesn't really tell us anything about either the big picture, or help people whose audience does include a lot of IE 11 users.
My clients all default to using IE 11, which is pretty standard in enterprise. Web developers might be using Chrome and Firefox, but the ~50 year old CFO of <insert large firm> is using IE because that's what IT have as the default because they have to support a ton of curf that only works in IE. If it doesn't work in the default browser the user won't use it and IT won't accept it.
It's a miracle that we can use flexbox as the bugs in IE11 have easy mitigations and most IT departments have at least upgraded to IE11 in recent years.
Windows7 had 6.8% of all sessions but seems like most of them are using a modern browser.
All really good signs for web developers out there!