Well we have to remember we're not necessarily limited to what's land-locked (or limited to specific locations for dungeons, we just went to part of Xelphatol after all.) and if you look at the world map the section slotted off for Gyr Abania is much smaller than what was slotted off for everything in Heavensward. (Not to mention stuff that isn't represented on the world map like Sea of Clouds and Churning Mists)
And with the addition of swimming (being locked behind MSQ no less) as well as retaining flying, there's two avenues to have more landmass than is actually shown on the world map.
It's not that difficult, the bad experience is probably shaking you more than anything else, the biggest thing is not to panic. Additionally, you've got the penalty of being down a member. And we don't know what role you were missing so if you were missing a healer or a tank that would further exacerbate the problem. You can work around missing a DPS in a lot of the dungeons in the game, but not so much a tank or healer.
Oh I thought the defeat was primarily because of me, and then I wasn't too fond of trying again. We didn't have a healer cause he quit. So we had me as a ranged DPS, a tank and someone who was making spells from afar.No more than regularly. It's just a matter of knowing what target to focus your attacks on at the right moment, and this is a universal skill that you'll repeatedly come back to. As a general rule, you should attack adds as they appear. If a new target appears on the boss during a fight, like the tail in this case, you should make sure to destroy it. These are small details that just make the tank and the healer's job easier. It's very possible to ignore the adds and the tail but still beat the boss -- happens all the time, actually -- but it becomes much more difficult for the tank to survive over the long-term of the fight.
But you were never going to win that fight with three party members. That's the primary reason for your defeat.
I will try the dungeon again in a moment.