The problem is the law of diminishing marginal utility. Translating from dollars to utilons is not straightforward at all; how much utility that dollar gives you depends on factors like how many dollars you already have, how much you owe, what services you can sell, and how much you know about what to do with money. For that same reason, utilons do not add up linearly by giving you a second, third, etc., dollar.
Right; assuming (falsely of course) that humans have coherent preferences satisfying the VNM axioms, what can be measured in utilons are not "amount of dollars" in the abstract, but "amount of dollars obtained in such-and-such way in such-and-such situation". But I wouldn't call this "not being meaningfully comparable". And there is nothing special about dollars here, any other object, event or experience is subject to the same.
As per a recent comment this thread is meant to voice contrarian opinions, that is anything this community tends not to agree with. Thus I ask you to post your contrarian views and upvote anything you do not agree with based on personal beliefs. Spam and trolling still needs to be downvoted.