chapter 274, page 3. Filth shatters his hand trying to punch Yujiro
absolutely and utterly inconsequencial to the argument at hand for 2 reasons:
1) Yujiro gets hit in the Frontal Bone area (slightly to the side, but still frontal bone), which is stated in-universe to be the hardest part of the human body and to shatter metacarpal bones of even comparable fighters just by virtue of its higher toughness
2) The Yujiro who broke Filth's fist is much stronger than the one Doppo fought, Yujiro is stated to grow stronger at an insane rate, in the time it takes Strydum and Baki to exchange a few words, he's already grown stronger, which means that he would have grown stronger in the time between his fight with Doppo and his appearance during the MT. This isn't even out of the blue, 'member when Motobe tagged and was generally heavily implied to be equal to base yujiro? Bember when Motobe's whole body was overpowered by the Yokozuna's pinky finger? Yujiro just pops up and essentially snaps the Yokozuna's spine, that ought to give you an idea of how much stronger he got, or did Motobe also get weaker?
chapter 218, page 16. Doppo says Filth was too strong and his body instinctively used a technique
I'm not kidding, this is what page 16 looks like on Mangasee, unless you mean page 15? Where Doppo says "I took so many punches that my body instinctively used the Sanchin technique", which is nowhere near an apology nor him saying that Filth is too strong.
Fine, let's steelman your argument and say that yes, you've proven that Doppo during the MT was weaker than pre-MT, what about NGB? Where he's implied by Katsumi to be stronger than he's ever seen? Where he's stated to have embarked in a special training journey and to have gone to "seek greater strength"?
There's way too much proof supporting Doppo not getting weaker and any proof of him doing so can easily be explained away