But drag isn't their name. While I have clue what their real name is, their user name is Dragon Rider, not drag. If you look at their display name, the drag part is in parentheses the same way gender tags usually are, like (he/him).

If drag said something like Dragon Riderself, that would be speaking in the third person.

And, yeah, I know that choosing a shortened version of one's user name as a person-independent pronoun is going to be confusing as hell. It looks like it's a dimunutive.

Even in your comment here, there's another telling difference. Noelself. You capitalized it even in the middle of a sentence. Dragon Rider doesn't capitalize drag (not usually, anyway, and I've interacted with them a good bit) except at the front of a sentence.

Again, it is confusing, at least at first. I've gotten used to it mostly, and it scans as a pronoun for me now.

Which is part of the point of PI pronoun usage, in my opinion. Ignoring whether or not it improves a person's ability to function without internal distress, which is an important factor in respecting pronoun overall, the fact of them serves to have us reexamine exactly why and how we think about labels, specifically pronouns and gender labels.

But, I'll also repeat, "unnecessarily" cluttering up a sentence is a value judgement, and while everyone has that right, it does indicate a degree of bias in thinking. It assumes that you have the authority to decide what is and isn't useful about another person's gender and pronoun/label preferences.

It could also be argued that a single word being used as a pronoun instead of the dozen or so in common usage is de-cluttering. If there's only one word to keep track of, that's a lot simpler than shifting between they/them/their. We're just not used to it, so it takes extra effort to parse. That's not the same thing as clutter though.