As a beginning VIM user I started out with the stock keybindings idea. After using it for nearly a decade, my finding is that it's like learning multiple spoken languages. It's not hard to switch context and use vanilla VIM despite normally using lots of customization. But, I do try to keep things idiomatic and predictable and not override frequently used key bindings.
This has been my experience as well. My vimrc is full of little niceties that I could live without, but if I end up in a vim without my shortcut keys I'd be like 'Oh this again I guess I have to :bn :bn instead of <C-q><C-q>'
I haven't really forgotten any of the long form commands that I create shortcuts for, but it's really annoying using the long forms when typing them out over and over was the reason why I created shortcuts for them in the first place...
