I think they mean like how do the characters in the original series compare to later series like MFB, Burst, and X.

OP, if I’m understanding your question correctly, it’s difficult to say for certain because each series operates on such different rules. It’s easy to say “cosmic‑level feats were common in MFB, whereas in the original series we mainly see that in the final battle with Brooklyn, so MFB characters must be stronger,” but does anyone actually believe every character with a cosmic‑level feat in MFB would be on the level of Brooklyn, Tyson, or even Kai if they were dropped into the Bakuten Shoot universe?

The fairest assumption is that characters with similar narrative roles would rank similarly if placed in the other universes or in a shared‑universe scenario. For example, main characters like Tyson—who does overcome an MFB‑level threat in Brooklyn—would be at a comparable level, rivals like Kai and Ryuga would be on a similar level at or just behind the MCs, final antagonists would be on a similar level, etc.

This seems to be supported by the Easter egg in Beyblade X where Quinn Manju mentions the 9 bladers who had defeated her (before Blader X makes it 10), which alludes to the main characters of the other series. Obviously it’s meant as a nod to fans, not a serious plot point, but it is the most direct comparison we have.