The real problem imo isn't with the original monster trio, no the real problem is that Jinbe and Yamato sit in an awkward spot right now. The two won't break into the M3 that only consists of Luffy Zoro and Sanji (Oda won't allow it), but at the same time the two also don't fit into the Mid Trio who are far more weaker than them. I don't see Franky, Robin or Brook replicating the feats of Jinbe or Yamato, i.e. blocking a magma fist from akainu or clashing with hybrid Kaido head on. Both Jinbe and Yamato have feats far above anyone from the Mid Trio and i think that slotting the two into the mid trio would be quite disrespectful to them.
I think after Wano it would make more sense for the 2 to be in their own new category, consisting of a duo.
After Wano the crew strength dynamics could look something like:
1st Level (Monster Trio): Luffy, Zoro, Sanji
2nd Level (New Duo): Yamato, Jinbe
3rd Level (Mid Trio): Franky, Robin, Brook
4th Level (Weak Trio): Chopper, Ussop, Nami
Jinbe and Yamato most likely isn't Oda trying to disrupt the Monster Trio, but rather to add more strong and capable fighters to the crew that isn't just Luffy, Zoro, Sanji.
Cause right now the crew has always had a power imbalance problem where the Monster Trio are too strong compared to the rest- making them look bad and far weaker. Jinbe and Yamato joining should make the rest of the crew look a lot better beyond just the Monster Trio. The future Pirate King's crew shouldn't just be feared for the Monster Trio, the Yonkos already have that dynamic- no it should be better. And having strong people like Jinbe and Yamato should help with that.