Not just ISPs; those using DNS-based adblockers (pi-hole and the like) will be impacted too (from my understanding.)
I think you missed the point of the parent comment, it wasn't that only ISPs poisoning DNS are impacted it was that this solves that problem for the vast majority who have no clue, excepting those who do the exact thing you describe and understand how to point it at their pi-hole.
But I strongly suspect we're in the minority and that something like this is the easiest -- and quite possibly the only -- way for many users to avoid DNS poisoning by ISPs.