URL autofill needs some work
As others have mentioned, the URL autofill has some problems. The main problem I see is that it isn't learning my habits in a timely manner. For example, every time I start to type the URL for one of my most used mail sites, it autofills the site for the MLB. I will never, under any circumstance, visit the MLB web site. After several days, my mail site should already be autofilling at the point that I type "m" into the address bar. The fact that it doesn't is problematic - I mean, come on, even IE has that feature. It's a no brainer.
Additionally, such unwanted sites in the drop down list are SUPPOSED to be deletable--when you see them in the list and hover over them, there is supposed to be an "x" allowing you to remove them from the list--however there are some, like the MLB site, that appear to hard wired in to the address bar! They are impossible to delete - no "x" shows up when you hover over that damn MLB address!! What, are they paying for that? It's annoying that the browser isn't learning, but it's even more annoying that I can't delete sites that have no place in my browser. I might not be so annoyed if it was something I didn't hate as much as baseball. But I can't swear to that.
You claim this browser is completely customizable, but so far, it hasn't really proven itself.
Calm down, you simply have mlb.com in bookmarks (Some are sponsoring Vivaldi and are added on 1st installation), and you surely have setting/address bar/autocomplete set to always prefer bookmarks. Edit your settings and/or bookmarks.
The main problem I see is that it isn't learning my habits in a timely manner.
There is no "learning your beloved URLs" feature in a browser. That is your misunderstanding.
The browser shows the typed URLs, bookmarks and the history's URLs.
I dont know yet how they are sorted.