I agree. Going forward I hope they'd consider making dungeons have side rooms and maybe even optional bosses. As a tank main, running in a straight line until you can't go any further, waiting for the mobs to die(rinse and repeat)started to get really boring early on in Heavensward. I'm hopping they start to add variety and cool offshoots or things to explore or interact with.
I understand that offshoots need to be rewarding by providing optional loot, currency, or some other reward meaningful enough for players to care about doing them. Otherwise it'll just be a race to the end regardless of how many optional things there are to explore. It's a balancing act, but going into the game's second expansion players are eventually going to get tired of the same dungeon design and demand something different, even just slightly, so that things stay fresh. In terms of optional bosses, the FF series is the king at providing them, so this shouldn't really be against their design philosophy.