Jinbe and Yamato joining the straw hat crew my not shake up the monster trio dynamic, but they should expand the crew's main combat force. People give the evidence that because neither Robin nor Franky disrupted the monster trio in the past, whoever joins in the future won't disrupt it either.
But i think that instead of looking at the monster trio as just the top 3 strongest straw hats, we should actually look at it as the crew's main fighting force. Luffy, Zoro and Sanji always gets fights in arcs, they have to and need to be the strongest, not just because they are. Luffy fights the big bad and main antagonist, zoro fights their number 2, while sanji fights their number 3. While both Robin and Franky were strong and were on par with the monster trio when they first joined, the real reason why they didn't keep up and eventually got put back into the mid trio is because neither Robin or Franky are combat oriented or have shown the history to be known for fighting. While Robin as Miss Sunday was strong, she was never a main combatant for crocodile and baroque works. Similarly for Franky, who was strong as say cyborg, was just a gang leader doing petty crimes, not a fighter by nature.
In contrast, both Yamato and Jinbe have a long history of fighting. Jinbe before joining the crew, before he even became a Warlord, fought and injured vice admiral Strawberry, and jinbe's reason and rise to warlord was because of his monstrous strength (jinbe got 76 million on his first bounty, almost the same as Sanji's and higher than Zoro's first bounty), he's been fighting the navy for a long time. Similarly, Yamato have fought Kaido many times, and acted as Onigashima's body guard while Kaido and the rest of the commanders were away in raids and expeditions. Kaido even uses Yamato as a test dummy for the topi roppo to see whether they have the right to challenge a All Star.
So when both Jinbe and Yamato join the crew, it wouldn't make sense that their expertise in fighting would be taken away and just be dumped in the mid trio where they don't actually fit. The Mid Trio is more like the Special Powers Group, Robin is Hax for fodder sweep, Franky is their mecha pascifista and plays as a second gunner to Ussop, while Brook is there for crowd control with his ice freeze, soul attacks and music hypnosis.
So instead of thinking at the monster trio will be disrupted becasue of insecurity or won't because of elitism, i think it actually makes more sense to have it expanded from the m3 to the m5. Luffy, Zoro and Sanji can keep their positions and get the 3 most important fights. it just means now that Yamato and Jinbe can get fights against the 4th and 5th strongest enemies.
The Straw Hats will be facing more Yonko, WG and Marine headquarters caliber enemies from now on and after the Wano Arc. It makes no sense that the later enemies the crew face will be limited to having just a Top 3 and no more strong fighters, considering how big the size of their organizations are.
If the crew doesn't beef up with more stronger fighters now, then how are they gonna match Teach's crew 1v1 when 7 out of 10 of the crew aren't strong enough, when teach has been recruiting stronger people like kuzan and level 6 prisoners from impel down, to the point where he has ten titanic captains. Is the Monster Trio supposed to take on all of them by themselves if the rest of the crew can't? At the current rate, the rest of the straw hats are underpowered and god knows how much plot would be needed to win.
Adding stronger members like Jinbe and Yamato to the crew now would be a good investment so oda doesn't have to resort to so much plot like he does to keep weaker members like Nami and Ussop from dying to stronger enemies. I mean did anybody like how Nami and Ussop couldn't take out Page One and Ulti, so Oda had to bring in Big Mom to do it for them?