where to draw the line?
Just taking whatever is easier. If your changes are easily packageable, then it should be a package. Changing systemd is probably not easily packageable. It's probably possible, but it's something where its not worth the effort.
Removing snaps? I feel like I'd prefer Mint to package its stuff as a package and leave removing snaps up to the user. But I vaguely remember that mint changes some repos too?
I actually like JS too. It is second to python in ease, but way better in terms of tooling and eco system.
The JavaScript eco system has some issues due to legacy baggage of browsers and design issues with node, but beyond that, the tooling is amazing and powerful.