And they also agree that…the answer to “is funner a word?” is yes. If you want to consider “fun,” as an adjective, a word, then “funner” is indeed a word, as is “funnest,” per normal rules of adjective formation.

Yes, 'funnier' is indeed a legitimate word in the English language. It's the comparative form of the adjective 'funny,' following the standard pattern for forming comparatives: Despite its regularity, 'funnier' often raises eyebrows.