I was an OMZ user pretty much since I adopted ZSH many years ago. I never really experienced much of the slowdown(s) that people tend to complain about. Even still, getting my dotfiles set up on a new machine was always a little bit of pain. I'd try to install OMZ from my OS' package manager, remember that that rarely worked perfectly, gone back to OMZ's webpage and copied the cURL command... the fought with FZF shell integration for about an hour. Finally one Saturday I just stripped it all out. I went with raw ZSH and Antigen for the few plugins I care about. Spinning up new machine is now painless. And I always like simplifying things.