GP most likely meant it was a solved problem from the user's perspective. Autotools might be "horrifying" for the programmer (IMO that is an exaggeration, AT isn't that bad, with the potential exception of libtool) but it provides by far the best UX for a user (that knows how to use a command line and what building from code is, not your average grandma :-P) compared to everything else out there.

However one important aspect here is that there is no reason for Autotools to be what provides the `./configure && make && make install` UX - the GNU standards (not sure the exact name) describe the UX itself without mentioning anything about Autotools so any other approach to implementing it would be just as valid. However in practice whenever you find a configure script in the wild it is either Autotools or a hand-made one (that more often that not misses some of the GNU standard stuff).