He's right. Prime WB and old WB had generally the same amount of power(his power was never stated to have decreased). The problem with old WB was that his physical health was at such a low, that his body couldn't keep up with this power for it to be as effective as his youth.
A Quake from old WB would be about the same from young WB, young WB would just be able to use more of them without problem on a more consistent basis. Admirals have shown to be able to clash and match his power, and the members of that trio have been shown to be able to clash with Admirals.
That would mean that each one of them would be able to contend with WB's power and push him. Two of them would be able to push him even further, and probably defeat him. A third one just stacks the math in their favor even more. Each of them are already in his general level, add three of those, and you'll have an edge away from WB.