Assume they mean having to recompile the AUR package they were trying to install using yay.

If users mental model is mostly "yay is like pacman but can also install packages from AUR the same way" wihout thinking deeper about the difference then I think it using it is very risky and that you should just stick to pacman + git/makepkg. Only consider helpers once that's become second nature and routine. Telling people to "just yay install" is doing them a disservice. An upgrade breaking the system isn't even that bad compared to getting infected with malware due to an old package you were using being orphaned and hijacked to spread malware or getting a bad copycat version due to a typo.

I think EndeavourOS is doing users a disservice if they provide sth like yay preinstalled and ready to use out of the box. It isn't installing packages from a shared repo: It's downloading code from arbitrary locations and running it on your machine in order to produce a package. Being able to read and understand shell script (PKGBUILD) is kind of a prerequisite to using it safely.