True.Did he? This is super weird but I'm finding conflicting data on what the gap on the Iseran was. Anyway, I don't think that should count. The main gc guys clearly could have gone faster but were happy letting De Plus do the work with the descent and the flat before the final climb still to come.
But you can make similar arguments fairly often when the biggest gaps on one climb happen. In the case of Pogacar, he just took off and within 15 seconds people behind were thinking about 2nd place. Doesn't mean he wasn't insanely strong, but the time gap was probably a bit inflated by tactics behind. Nibali on Hautacam is a bit similar in that they didn't give a *** about limiting the gap to Nibbles.
Having a gap of 1 minute between the 1st and 2nd best GC rider is mostly a bad criteria I think cause it strongly punishes for having a really strong 2/3 riders in the race.