I do wish they carried through a bit more with the Malon. When we first meet them, it's an arrogant freighter willfully polluting an inhabited area; when Janeway suggests a fix for the theta waste, they state that their scientists would probably love it, but they themselves refuse to inform them since it would end their jobs.
And then... it ends there. When we next meet the Malon, the solution to pollution isn't even brought up - Voyager simply assumes they'll have the same attitude and doesn't even try to change their minds, other than some sneers from B'Elanna about whether their utopic home planet is worth the pain they've brought to others.
But Fesek would be the perfect person to bring the advancement back to his society! He states outright he's not a career hauler - he's a sculptor, who takes a turn on the freighters out of a sense of duty and obligation to his home planet. The pollution is shown as an unfortunate side effect that they nonetheless attempt to mitigate by finding empty places to dump.
Fesek has no need to protect his job - he would likely be overjoyed to find a way to maintain his society without the onerous and dangerous duty of theta radiation dumping. His son could pursue a safer career, one without scarring or "occupational hazards".
Alas! I'll just assume they sent it with him off-screen and after a period of political turmoil (let's be realistic) Malon Prime became the true utopia it was always meant to be.