LOL. My experience with an average of 5-6 backgrounded vims *per each named tmux session" which I use to keep track of different source files I'm working on goes against this. Sure, I can use vim's windows, but I don't want split screen usually (I'll use the other terminal I have open if I do). I don't use tmux's windows either really. It's more a way to preserve session when changing workstations (these are remote terminals), and preserve against network drops. I use each tmux session as a contained work environment for the most part. I do all my software development using vim on a remote server, and have for most of the last two decades. I've worked with numerous other developers that work similarly for professional projects, personal projects, or both.
Let's just say that there might be people that use the combined features of terminal applications, terminals, and remote connections in ways that you might think were rare, but actually have large following and leave it at that. :)
But in the end it's not about whether it's efficient, it's about whether it's rare, and I think it's not from the different vim users I've encountered, which may be an entirely different subset than the ones you have.
There are benefits to being comfortable in a somewhat stock Vin, and there are benefits to having it highly customized. I find the benefits imparted might be outweighed by the discomfort when it's not as you expect if your work flow forces that situation on you, so as my work flow has changed with the type of work I do, I've tried adopting different vim strategies.