I wonder, could the waveguide technology in these make them more prone to treble troubles in an untreated room?

Maybe this is why opinions on their highs could be a bit inconsistent and contrasting?

Unless I'm missing something, it essentially enables the tweeter to send out consistent sound in a much wider angle, whereas a regular monitor would sound more muffled and center-lacking off axis.
Which I would assume can result in more/stronger possible reflections from untreated surfaces?

Plausible? I'm fairly inexperienced in the grand scheme of things, so...yea.

I'm not knocking the amazing waveguide technology, for the record. It achieves its intended effect superbly.
But I too have noticed that my JBLs sound a bit harsh at high volumes (untreated room; need to fix that), whereas if kept quiet they're some of the most balanced speakers I've ever heard.

....oooooooor It's just my untreated room in which any speaker would sound harsh because the room... is untreated.