sudoedit is used by many people, and setting a different shell with -s seems like something that would cover a number of edge cases, yes, but writing a new tool just to add "-s" is obviously silly. Nothing in this particular CVE touches on anything that seems particularly obscure to me.
The last major sudo bug was in the PAM code (which lead to the creation of doas), which is something many people don't need, but also something that many others do need.
And writing separate tools would be the equal (or more!) lines of code and an equal amount of bugs in total (or probably more, since people will be reinventing stuff and there will be fewer reviewers per line of code). This isn't reducing complexity, it's just spreading it out.
For what it's worth, PAM is also not invited to my parties, for all of the same reasons as sudo was shown the door. And what people want PAM for is mostly solved with SSH certificates.
>writing separate tools would be the equal (or more!) lines of code and an equal amount of bugs in total
In total, yes, but crucially, not all on your system at the same time.
If doas doesn't cover your edge case, then the responsible thing is to make a new tool which covers just that, and not to shove your complexity into a critical security component that the other 99% of the userbase doesn't need. Remember Heartbleed? The entire internet shat its pants because of a vulnerability in a feature that no one uses.
Failing to uphold that principle over and over again leads to broken, unreliable, insecure programs. This is why everything is on fire. Not C.