Sorry in advance for the following text: You did realize this just now for the first time? 😕Firstly I don't see any contradiction to Nephs initial point here: Given it all happened under influence of a force nexus, with Obi-Wan outright telling Anakin to utilize the force energy of the place, it seems to be unlikely, that Anakin could do something even remotely compareable apart from the nexus.
Secondly, I may point out, that you seem to have overlooked a little detail. Neither Obi-Wan nor Ahsoka are shown to receive any kind of "boost" in ability from the place, which kind of contradicts your assertion that it boosts the abilities of all force users present. Furthermore, even Anakin's own "boost" doesn't seem to be permanent, since he is pretty much inable to control / defeat the son throughout the rest of the episodes. In fact, the only other situation, in which he shows some unusual amount of power, is, when he "revives" his Padawan.
That being said, there is no evidence to conclude, that the children or the father receive a boost in force abilities, that is anywhere close to what Skywalker gets. In fact, as the father indicates multiple times, Anakin's unique nature as Chosen One is, what enables him to keep both children in check and thereby maintain the balance. If we can trust the fathers statements, Anakin was born to fulfill that task. This idea alone serves as a contradiction to your personal interpretation.
Combining this with the fact, that the two other Jedi didn't receive any noticeable boost in terms of force abilities, one might come to the conclusion, that Anakins performance was far less impressive than it seemed, because the place simple amped him more than it did boost the abilities of the two children, due to his very nature as Chosen One.
Furthermore, I still don't see any chance to draw any conclusions from that scene, that might be applicable to a versus fight not happening on Mortis.