... but I would still get advantages in terms of speed, maintainability, etc. from using a modern web development environment that I see no reason to give up. There are things like cache-busting hashes, linting, splitting js code in modules and using variables in SASS for things like colors, that to me are mandatory in a professional practice.
That's not the requirement I'm talking about. It's "multiple developers you don't know, of varying experience levels, will work on this project over the course of years".
They're going to clone the repository and have to make changes. Ignoring your stack is not an option. They have to figure it out, or throw it away and rebuild something else.
They'll be the ones paying the time cost of all the advantages you get by doing something complex but easy for you.
You may say this doesn't apply in your situation, and maybe right now it doesn't, but it almost always happens in any successful project eventually.
This might be technically true, but is not true in any meaningful sense if another developer ever has to work with your code. They will have to deal with all your baggage, and their job will be much harder because of it.