Advertisements or recommendations in Windows 10 are definitely helping Edge
For example Wikimedia shows Firefox at 12%~ of desktop browser usage whereas W3Counter has it at only 6.1% and StatCounter 7.95%. With the latter two being JavaScript based.
I don't care about the loss of horizontal space most of the time. I have a 16:9 screen and most web pages grow vertically anyway.
As a matter of fact I use a vertical Windows taskbar as well, since it lets me have many applications open while still displaying their window titles. It's not usual for me to have 5 file explorer windows open, and their taskbar buttons won't combine.
I wish vertical tabs were a standard option on all browsers, especially on Firefox where you need userchrome hacking on top of an extension to get something usable — userchrome css is deprecated and going away, which means integration deeper than is offered by extensions will be necessary in the future.