Yeah that's true.

If the level geometry is mostly grid aligned (meaning few diagonals and such) you can for example put min_x/max_x to something small (0.01) temporarily, do a trace in x-direction, reset min/max, same for y, and use "target" positions to limit player movement. I do something like that in my sidescroller as it emulates a box (or in 3D cylindrical) trace more or less easily.