Worstgen

In one chapter Oda hypes GB and a month later in the very next chapter his hype is destroyed (their is a chance it might go back up).
Hype:

1. He is shown to have defeated 2 All Stars, Queen and King, and other fodder of the Beast Pirates in Udon. We see no cuffs on either YC and we see sake available which is shown to indicate that they were recovering (can't understand how even after a week BPs are free enough to do shit like this, wtf are the samurai doing). We also get his comment about them being mere commanders. There are a few things to be noted here though:
   1. We have zero indication of either YC being an awakened Zoan (the thing that is mostly associated with extreme recovery). They are ancient Zoans though who are known for their toughness (the biggest clarification is Zoro saying that the dragon and the dinosaurs soak up damage like nobody's business).
   2. Extension of previous point, they are not said to possess super regen, maybe in beast form they get some boost in regen based on specific animals. King is not shown to have his fire burning behind his back.
   3. The YCs were destroyed in their fights against SHs. Queen lost his mechanical arm and King lost his sword and wing. They were not in their best condition to fight an Admiral.
2. We see the whole/a big chunk of Udon covered in vegetation when it was a wasteland before, which many correctly guessed the Admiral to be a forest or similar devil fruit user, probably awakened with the enormous area of effect.
3. Arguably GB has a black blade.

De-Hype:

1. GB is shown to use some tree mode or thing, I think Enel is the only other Logia we have seen who has gone into some sort of a specific transformation using his element. In this form his branches are damaged/cut by Scabbards and Momo, none of who are stronger than the YCs, the same Scabbards were brutally wounded by Kaido and also had only a week of recovery. How are weaker characters able to do more damage (it may not be much) on panel than stronger characters.
2. GB gets his big head knocked to the ground from a no-name ACoC attack by Yamato (not the biggest problem but still).
3. His comment about hierarchies bringing stability which I think ties to his comment saying mere commanders.
4. Sabo and Co. saved Kuma and escaped. (Luffy did the same to BM and the excuse of the Admirals not being able to go all out is already there in the manga.)

I think the Scabbards, Yamato and Momo should not be able to hold off GB. We have zero indication of the moves doing any lasting damage. The points being used to trash or de-hype GB are not very solid points. GB's fight against weakened YCs was off-screened so we cannot measure the Scabbards and Co. performance against anything. GB is a logia and while haki lets you hit the main body, there is the possibility that not all the vegetation is directly attached to GB's body. He is somewhat of a mixture between Pica and his giant form and Smoker in my opinion. For example the branches cut by the Scabbards were not part of GB's body but his head which was attack by Yamato was attached to Yamato and that's why he commented on Yamato having a strong haki and the attack hurting GB.

To me GB has the potential of having the highest recovery and regen considering he has probably the most powerful plant type fruit (like the magma of plants) and his special property is regen and durability like destruction for magma. We have still to see him use his sword (might be a meito, although Tashigi said that all these swords are in the hands of pirates or bounty hunters).

P.S My points above about YCs not being in peak condition does not mean that they would have won. I am just saying that Marco and King got hype and portrayal from Yonkos, King also had the not losing to anyone thing. I just don't see any YC1 getting neg-diffed by a Yonko or Admiral. We know Admirals are very strong, even Marco and Vista were not able to do much to Akainu. 2 fresh YCs should give at least a mid diff fight to any Yonko/Admiral. GB's seems like an arrogant, trash-talking sound of guy so even if he won high diff he would probably say such humiliating things. I hope the anime will clear things up.