Until vim 8, everything in vim ran in a single thread with little or no cooperative multitasking. So if you have a handful of plugins that do any non-trivial thing with the contents of a buffer in real time - dynamic syntax highlighting, running an external process or other such things - pretty soon those milliseconds add up and there is a visible delay between your typing and the on-screen cursor. Vim 8's background tasks were created precisely to deal with these sort of problems.

Even basic highlighting and the mentioned relative linenumbers will put VIM to sleep. Which honestly is absolutely pathetic (and a know problem which was never fixed).

The file opener/finder ctrlp is kind of slow as well (there is a different search engine for it which is an order of a magnitude faster).

I really like the vim keybindings and just use ideaVim plugin for intellij which can do all the vim stuff i need and has the ide functionality on top. And it is faster as well (at least it can do relative line numbers without dying)

Yes, just look for the most popular plugins. Or try using a popular "dotfiles" configuration, compare it with a raw Vim and it's really slow. With sublime you can have a lot of plugins and it doesn't affect the speed.

The plugins the OP was using are pretty heavy, the real question to ask if they're necessary. Just using the default netrw over Ctrl-P is a great alternative with little or no cfg. Syntastic is overkill IMO, just use an IDE at this point - Also using silver search is great, but not necessary if you understand how to Grep.

Honestly the author just lacked the time and knowledge to go ahead and learn basic bash tools and utilize them.