There's no doubt some fuzzy math involved to extrapolate inflation over the course of 50+ years, but I don't think that invalidates the fact that minimum wage has objectively not kept up with inflation even remotely.
The federal minimum wage has been stuck at $7.25 since 2009, and a handful of states are only just now breaching $15/hr. At this rate by the time a federal increase happens we'll already be another 20 years behind.
Worse yet is that labor data shows that more and more adults are working in minimum wage jobs, so the talking point of "it's just summer jobs for teenagers" and "it's entry level work to move on from" is very out of touch with reality these days. There are millions of people trying to survive on these wage levels and without benefits and it is not working.