I agree that the arc opponent theme plays an important role in keeping M3 a relevant concept but that's surely not the only thing that keeps it going on.
I can't disagree that Oda slightly altered the dynamics he usually follows since the introduction of WG after TS. However, I don't think the crew's dynamics were actually touched, not drastically at least. Though he was the strongest on PH; Vergo wasn't the main arc boss. He was an outsider as far as it concerns what the SH crew was really after. CC was the main villain at PH followed by Monet and that's who Luffy and Zoro fought.
Most of the recent arcs involve a lot of heavy-hitters who deserve some serious focus. It's understandable that Oda is taking the focus off the SH to highlight these heavy-hitters. It's refreshing that he is taking a different route than the usual SH-centered theme that he's been following for years but I doubt he's got any plans to make SH's less relevant. As a matter of fact, it's been mostly Luffy and Zoro who the Wano arc is revolving around. I am sure Law has a vital role to play in Wano but I am also sure he and the other WB members will be eventually sidelined.
Thinking back, we all thought Law deserves to defeat Doffy the most back in Dressrossa days but he had to settle for Trebol. Although he played an important role, he was ultimately sidelined and became a cheerleader as Luffy and Zoro take on and defeat number 1 and 2 main bosses of an arc that centers around him more than anyone else. The same happened to Bage back at WCI; he started as a partner in the BM assassination team and ended up in the cake delivery team.
If they were sidelined in their own arcs, they most likely won't be able to replace the SH's as the most relevant in the arcs to come. The SH's will surely but eventually take their spots back as the most relevant bunch in no time.
@Kishido I hope I am not derailing your thread.
Even if I were to agree with you here (highly disagree since Vergo was much more important to the saga's narrative than Monet (arguably Doflamingo's most trusted and strongest underling, working as a double agent in the navy) with Law cutting the SAD factory, and Gamma Knife was clearly defined as part of the reason Doffy fell, including how the world viewed it as a tag team effort. It's absolutely nothing like Bege's situation), Sanji is nowhere to be found in your post and for a reason, without him being heavily involved there is no M3. Let's see what happens on Wano but I have my doubts he gets to be higher in the pecking order above Law, Kidd, and possibly others.
One thing that gives some hope towards the M3 dynamic is that Oda is using up nearly the entire WG here on Wano for some big finale, so there may be some room left after, but that's purely speculation. Since FI it's been shoved aside and it's just as possible it'll fade into irrelevance for the rest of the story especially with Jinbei's addition. We may never get a traditional One Piece arc ever again.
I guess my point is the thread title should be "the Monster Trio will come back" at best, because it's been MIA for a decade or so. "Staying" implies it currently exists which we've honestly been given no substantial reason to believe.