Having several copies of a GIT repo for different branches is a viable strategy as long as one does not do force-pushes.
In any case, I've made a speedy replacement.
Fair enough but if you allow me to suggest you this: don't do it for the readership, do it for your own skills of eloquent and convincing writing. Even if nobody ever reads it, developing proper articulation and being exhaustive in your analysis will only make you smarter and better at what you do.
This is unsolicited advice though, and I apologize if it's misplaced.
I just always found it cleaner to have several directories on the rare occasion I need to work on several branches almost in parallel.
And let's face it, most of us don't work in a repo that is 100GB or above. Even if it was a 10GB I wouldn't care one bit and can easily have 20 copies of it temporarily.
Your colleague, well, maybe you as well, could instead make use of 'git worktree'
https://git-scm.com/docs/git-worktree
It allows exactly that, use a single repo yet have parallel checkouts in separate directories.
I would advise you to instead eliminate class prejudice from your writing. A common type of class prejudicial remark programmers make is sniping at "spreadsheets", i.e., the programming tools of the outgroup not initiated into nonsensical programmer esoterica, aren't those nonprogrammers benighted and silly? But really, spreadsheets are so valuable to them because they're one of the only ways they can tell a computer (a machine that ostensibly serves them) what to do without interacting with the priesthood.
But you shouldn't listen to me either. I'm just some fucking moron on a website. Please understand this.
Here's a more concrete thing - I work on a product that took years and a spectacular sum of money to get going on the data space (all it does is land CSVs into S3 and then load them into a database every day, < 10GB per day). The original designers decided that the entire thing should be powered by spreadsheets, so we now have about 10 full-time staff editing spreadsheets that trigger build pipelines, one of which I believe has 400 separate worksheets in it.
However, you are right that, broadly speaking, I have no idea what I'm talking about. I have made peace with this.