4 games that i ran and played most are D&D, WoD, 7th sea and GURPS.
Only thing i took away from runing long campaign in GURPS is that i don't wont to play or run GURPS ever. Haven't touched that system in 17 years. To be perfectly honest, i can barley remember any rules or how that game works any more.
For D&D, playing and running different editions (2nd, 3.x, pf1, 4e, 5e) was more useful than playing or running other 3 games. My D&D games are very different than my WoD games which are different than my 7th sea games. There is almost no spillover from one system to another in play style, themes, plots, pacing, campaign length, amount of prep work etc.
One good thing about playing with same group for very long time is you can see how much your games change over the years, even if you still nominally play same game. Did we play other games? Yes, we did, but it wasn't biggest impact on the change (for better). I would say, i'm much better DM and player today than 10 or 20 years ago. It's mostly due to growing up, maturing, getting better at some skills i picked up trough life: from being a junior army officer, calm leadership under pressure, discipline to do boring work, clear communication of intent, consistent and fair rulings, decisiveness, and the ability to adapt plans when naughty word goes sideways. From corporate sales and management- active listening, reading the room, improvising when things go off-script, aligning different player motivations toward a shared goal, negotiating outcomes that feel like wins for everyone, and maintaining momentum without forcing choices, curiosity about my players, a genuine interest in what excites them, humility to accept feedback and admit mistakes, system literacy sufficient to make confident rulings even if i’m wrong, again consistency so players can trust the game, courage to say “no” when necessary and “yes” when i think it will make the game better, emotional intelligence to manage table dynamics, resilience when sessions don’t land as hoped. Finally, from being a parent- patience, empathy, emotional self-control, encouragement over punishment, knowing when to be firm and when to be flexible, celebrating small successes, and prioritizing trust, safety, and long-term fun. What i want to say with this too long paragraph is that we all pick up different skills and behavior patterns trough work, other hobbies, and life in general, that make us better players and DMs, even if we only ever play or run one single game (or single edition of one game).
Personally, i know for sure i'm not best DM in my social circle, let alone compared to some others out there. But i don't need to be. I need to be just good enough so that my players have confidence in me and know that they will have fun playing games i run.