I mean, design philosophies for both games are different, sure 2D Mario games could learn a few more things from it's brothers but technically, he's almost asking for Mario to become a DK Clone.
I wouldn't exactly say he's asking for Mario to become a clone of DK. Its more comparing the 2 together and looking at how they differ. Like with his points of each level being distinct from the other, Mario heavily lacks that. Or that soundtrack being so much more inferior in Mario. How well the levels in DK flow, their superior design, and overall story they tell. How vibrant and eye catching the art style and atmosphere is in DK. Mario can still be Mario, even with adapting to these strengths from DK (with a mario twist on them; within the mario universe). The 'New' series is like on its like 5th game that have been very similar to each other, I won't say its out of reach for fans to start looking at other series and point out how much they do this old formula better.