Jobs aren't being locked out nowadays except in optimization parties. With that said, it still remains advantageous to lock out jobs which are dramatically underperforming even several weeks into the tier. Why? PF inconsistencies. Did the Dragoon pick up their third damage down in P8S? It doesn't matter because you brought Dark Knight and Gunbreaker who can muscle through the DPS check with their extra 1000 DPS (less now with the buffs to Warrior and Paladin). Perhaps the biggest irony people ignore is it isn't the high end raid community who needs meta but PF who benefits from it. Party Finder has inconsistent players who collect damage downs, die to messing up mechanics or aren't rolling their GCD. You'll have healers spamming GCDs either due to playing overly safe or compensating for other players who aren't using their mitigation. All this results in significantly lower damage output.
To really emphasise my point. Party Finder is still tank LBing a mechanic (Cachexia 2) my group skipped entirely on the first week. We didn't skip it for several weeks after because we were bad, however the point still stands.
Cachexia 2 and War's Harvest are major choke points for PF. Having any DPS advantage that may allow you to skip them or compensate for the resulting deaths may be the different between clearing and hitting enrage. At least in the first month of any given tier.
Regardless, this isn't really an issue any longer now and the only restrictions people put up are ilvl.
How do you know this? You've never completed a single Savage tier on content. At best, this is entirely hearsay—which isn't saying much because we have no idea on the qualifications of those players. Speaking from actual experience, this never happened. The only time people made any sort of stink about your melds is during Stormblood Ultimates when the occasional DPS and Healer refused to meld Vitality, which made them squishier. Nobody was looking through your gear to check whether your i400 Omega Earrings were proper bis. They weren't doing it in Midas either when Savage was more on par with Ultimate level difficulty. Substats have never been more than a very small fraction.
Even if I took you at face value, you openly claim it was only ever a minority of players who bothered. So... who cares? It wouldn't be applicable to the argument I had with Jojoya earlier and what sparked this whole conversation to begin with: Adding raid equivalent gear to Criterion wouldn't make it mandatory.