I mean the main sticking point for the multipliers page is internal consistency. The statement comes from an approved source, the main issue to any multiplier getting accepted (as discussed on the multipliers page) is whether or not it should be considered hyperbolic based on the actual demonstrated feats.
In the case of Demon Slayer, the DSM is consistently treated as a big boost, so the positive case for it is solid. The main anti-feat I would consider would be the case of Mitsuri, who got her DSM mid-battle with Zohakuten and continued to fight it out in a stall battle. Although it has been argued that after Mitsuri unlocked her DSM we get a statement from Urami that Zohaluten was now dedicating too much power from their collective reserve to fight off Mitsuri, which indicates he likely wasn’t fully committing all his energy prior. Of course Zohakuten is also unkillable at that point so Mitsuri winning outright isn’t expected even with a big stat boost, although the counter-argument would be her being able to keep up similarly prior to unlocking the DSM.
So up to interpretation, although currently accepted based on the otherwise pretty consistent portrayal of a big stat boost across different characters when unlocking it.