You wrote a large reply, so I feel I owe you a good response. Honestly, I feel it's kind of, let's say, interesting, that I have to defend things like "maybe we'd like more than one font size". Maybe it's worth the sacrifice for having vim retain the same look-and-feel in the terminal, but to outright think that variable font sizes are inherently useless in a software program? Whose primary purpose is to edit text, no less?
Still, here are some examples of more functional ways vim could be better. Most of these are related to visuals, yes, because that's the main thing that plugins can't change in vim.
Examples:
1. Code folding is there to make it easier to scan code. Vim's folds take up a lot of space, and aren't very easy to scan. Yes, this is subjective - it's possible that for you, it's the easiest to scan thing in the world. But for me, the way many modern editors work is better - have a simple, colored, "..." indicator at the end of the line that has a fold after it. Simple, easy to scan, doesn't take up any more lines on screen. Minimal, in the sense of UI.
2. Adding some kind of info in the margin. Most editors add some kind of way to see folds in the margin. This is usually kept very tight, since all you really need are some dashed-lines and a "+" sign, perhaps. Not possible with vim. The closest we have is "foldcolumn", which a) takes up a lot of space, and b) is less visually appearling, making it harder to understand or use. Other info is also sometimes added, not just folds.
3. The project opening. While I love ctrl-p, especially over the alternatives, it has several flaws. For example, it's very, noticeably, slow. And I'm on small projects, usually.
But here's the bigger issue: the way ctrl-p in Sublime works is more beautiful, but that's not the only advantage. It makes it easier to see what file you're going to open. It makes it easier by doing things like bold-ing the letters that it's matched. It makes it easier by making the filenames "REALLY BIG", but still giving you the details of the file's location in a smaller font.
There are really many more issues I can bring up, but these are the keys. In all honesty, vim is a bad choice for most people because, to get it to the level of what Sublime Text or other editors do out of the box, you have to spend months tweaking vim. This makes it irrelevant for the vast, vast majority of people, which is unfortunate, because it has text-editing capabilites that are simply unsurpassed by any other editor.