I mean, is it safe to only train for under 20 hours?

You can't regulate people into safety. Its the CFI that decides when a
student is ready for a checkride. You can't automatically take the
checkride just because you meet the mins. There is no reason for the
FAA to tie back the hands of CFIs. There are some programs that can
produce 40 hours private pilots that are safer than 60 hour students
from other places.

-Robert, CFI