Revenge of the Round Arena!

[Yasuhiro]

Alexander Midas 6 was really daring
A corridor and then a mixture of circular and square arena's, the absolute mad man, how did the board room meeting go? Even the yes men didn't know whether to nod their heads.

[Moomba33]

I suspect they don't do more interesting arenas because the playerbase usually finds a way to exploit it. Like how at launch you could dodge Doom from Qarn's first boss by climbing on the rubble, or how players would drag the Relic Reborn chimera up the hill so ranged wouldn't have to move for Dragon's Voice, or how people would hide in a ditch in t5 to force Twintania to Divebomb from one direction and make it easier to dodge.
I don't see the circular arenas as a big deal myself but variety is always nice.

[Canadane]

I suspect they don't do more interesting arenas because the playerbase usually finds a way to exploit it. Like how at launch you could dodge Doom from Qarn's first boss by climbing on the rubble, or how players would drag the Relic Reborn chimera up the hill so ranged wouldn't have to move for Dragon's Voice, or how people would hide in a ditch in t5 to force Twintania to Divebomb from one direction and make it easier to dodge.
I don't see the circular arenas as a big deal myself but variety is always nice.

I don't really see a problem with out-of-the-box strategies like that.