Jan, like many others in the modern era, benefitted tremendously by still being around (and relatively healthy) when the division had basically become extinct. It's no coincidence a (let's be honest) very average fighter suddenly became a "world champion" after years of treading water during the same era when bottom feeder middleweights were jumping up a division and walking into title shots.
I like Jan and am happy he has made some money and gained some fame but I am also not buying into the hype machine that he suddenly became a world beater in his late 30s. Same goes for Glover who is at least more well rounded/accomplished than Jan ever was. These guys had both been around for YEARS and we had a pretty good idea of what they could/couldn't do but then suddenly, they're matched up with (as referenced earlier) a few journeymen MWs who are wildly overrated from the PR machine and they win. All good... but then suddenly people are saying Jones is ducking Jan and Glover would beat Jones in a rematch despite being absolutely handled by him in his prime? The recency biased is all too real.
Success in the current LHW division, just like the current MW division (where Derek freaking Brunson is ranked top 5), must be taken with a grain of salt. Any rational person can look at the rankings and see how paper thin they are (WW/LW getting there too) and that there is absolutely no doubt we are in one of the weakest eras of all time.
TL/DR: Anderson via murder. Jan is a likeable fighter but a glorified journeyman who would (and did) struggle in a deeper talent pool