Maybe for sysadmins that are always doing a ton of text editing on remote servers, but I haven't run into this. Even when I do work on servers though I don't have any problems using vanilla VIM even though my workstation has 70 plugins. I do take care not to override any of the base keybindings though. If you are overriding core bindings you deserve what you get hehe.
If you're talking about traditional UX values like intuitiveness, sure, vim UX is terrible.
But vim features tend to do very simple things, which are composable into very powerful mini programs in a lot of contexts. There's a sort of "discoverability" to them as well, in that if a key does something in one mode, it likely does something intuitively similar in another mode. All this adds up over time. I've got about 9 years using vim every day now, and the combined learning over that time has added up in a way that disposable learning like "how to use the X flavor-of-the-week plugin" would not have.
Another thing here is that the UX improvement of most plugins is only surface-level. vim features tend to be very simple, which means that when you understand it, you understand it. But vim users with a lot of plugins rarely understand what is actually going on when they use a plugin feature, because the features do too much. This means that they can't really use those features in, for example, macros, which loses you a lot of the editor's power.
1. Part of the joy of vim is not configuring it. A ton of the plugins out there exist because the creators didn't know that a feature already existed in vim, and many of them break existing keybindings. Beyond a few small configurations, I use vim as my daily editor largely untouched. A big upside to this is that I can log on to almost any server and have an editor that is pretty close to what I use anyway.
2. My configuration process is (assume you're in ~):
This works fine for pretty complicated configurations, but if there's something that can't be configured in a dotfile, I imagine it wouldn't be hard to add a ./configure script that does the rest.