Not all of those big AoEs have telegraphs. The OP’s concerns are right, though I suspect it’s because of his monitor and not necessarily the game. The game itself was designed in 21:9 (which is why you can force that aspect ratio in the video settings) and is meant to be played as such. Problem is, unless you have hundreds, if not a couple thousand dollars to spare, getting a halfway decent widescreen monitor is out of the cards.
Not sure I approve of the way they designed the game around that, but I will say, if you have one, it looks really, really nice. When I do big boss events like guardian raids and abyssals, I force the 21:9 aspect ratio just so I can make sure I see the entirety of the battelfield, even if it looks smaller on my monitor.
I don’t really know enough to be able to say one way or the other except that being able to see more of the battlefield is a clear advantage, particularly in PvP or dealing with those annoying long-range abilities with no telegraphs. That in itself tells me one of two things: either you’re right and it’s just an oversight, or it’s deliberate and they want us to use widescreen monitors that support it better than having the annoying black lines above and below when you force their aspect ratio.
See, that’s what I thought originally too, but I swear I’m not crazy, I read somewhere that the devs were talking about designing it around that aspect ratio. I’ll have to look into it and see if I can find that again - or I’m just crazy and I read an anecdotal forum post.