I get that people like Onslaught Fetch lands, but that was not even the first printing of the mechanic. Mirage block had fetch lands. I don't recall Mirage fetches being played really at all. So, while the power level was obviously raised on the Onslaught fetches, they weren't some original or novel concept that was added to the game. Fetches by themselves, are pretty much inferior to dual lands since they damage you and without the existence of duals could only pick 1 color type. So they are not independently powerful, or original.
They printed a card that was not as good and then later they printed a much stronger version witch now reigns supreme in basically every format. This is a sentence frame that could be used to define power creep, and the they dont power creep lands guy is saying it about lands. This is highly confusing.
You can claim they should power creep lands more I disagree, but I care about other formats and I am not ready to argue doing so would be bad for vintage, just for literally every other format except maybe pauper depending on rarity.
You can say they don't power creep nanland mana sources. This is true.
But no reasonable person can claim they don't power creep lands, unless the baseline for lands is bazaar and kind of workshop but academy exists so even claiming workshop has not been crept is tricky. I personally do not think these cards should be used as baselines any more than ancestral should be used as the baseline for blue spells but that is an opinion.