Hate to break it to you, but the monster trio hasn't existed for a long time now. With the introduction of the Worst Gen, even Zoro's spotlight has taken a hit thanks to Law. Punk Hazard he defeated the strongest opponent, Dressrosa took part in defeating the main antagonist, and now in Wano it's possible he'll be in the final battle against Kaidou, if not him Kidd is going to be either way. Sanji is just picking up the crumbs to find any relevant fight, and for a lot of post skip he's given the honours of playing the hype tool for enemies thanks to him being in the "just strong enough, but just weak enough" sweet spot.
I like the addition of the raid suit though, it was much needed for Sanji to remain somewhat relevant as a fighter on Wano, way too many hard hitters here otherwise.
But yea if you want to blame something for the irrelevance of the M3 you can thank the WG, too many strong/important individuals to fit into a scheme in order for the Strawhats to still get theirs like pre skip. We've moved past just the SH pirates at this point of the story, too many mouths to feed, that's hard for a lot of you to accept (understandable since that's what made people fall in love with One Piece in the first place).