Maybe that's an Asura thing, RMT-bought MLs are not a thing on small servers.
Maybe the small servers are different from each other, but on my small server there are LOADS of people with ML50 who have no idea what they're doing, because they botted and/or bought ML50. We have someone in my LS who's ML40 (or 45?) on a job and has only Ambu gear and hasn't touched basically any endgame at all.
I think the best suggestions for how to show someone is "gud" would be the thing people suggested about clearing content on many different roles. People who are REALLY good but only at a specific job/role don't impress me anywhere near as much as people who can swap from WHM to PLD to SAM to RNG to BLM on a dime. These people are, in my experience, exceedingly rare though. Especially those who actually know the detailed nuance of each job and not just "yeah I have that job, it's ML50 and geared, but I don't have the first *** idea what to do on it"
Everything else is cheesable and frankly, there are lots of people I've played with who have been carried HARD through a lot of content, including some of the hardest ***in the game. While the fights are very challenging, there's always a couple jobs you can throw an idiot on and they don't have to do anything too complicated while you walk their happy *** across the finish line.
If I had to pick something in the current game, I think the most impressive things to me ATM are the super hard master trials (maybe there's only 1 right now?), St5 Prime weapons, and R30 Nyame/all Ody bosses V25 (easy to cheese, but not on Carbuncle).
While prime weapons/Aminon aren't actually all THAT skilled/difficult to get, it shows me that you have at least some social skills to be able to (probably) regularly do well in Sortie and (definitely) clear HM Aminon a bunch of times, which is no simple task. Prime AG are quite uncommon on Carbuncle, to the point where I still turn my head when I see one and I'm surprised, even a couple years into the release of them.