We used to have nonlinear dungeons and we spent a lot of time waiting for new people to figure out which way to go, or wasting time killing unnecessary mobs (which now also don't give any rewards at all, making them even more pointless). Not every dungeon is three sets of

pack-pack-wall
pack-pack-wall
midboss

Some have three packs before or after the first wall, some have five packs with no walls and it's up to you to know whether the "standard" pull is two then three or three then two, or if pulling all five packs is doable safely or if it's a deathwish. The current dungeon formula is fine and is varied enough where it needs to be--namely, where bosses are concerned. They're runnable in a standard amount of time ranging from 15 to 20 minutes without having to stop to tell people where to go or what to do and that makes them good daily task fodder.

For those who want something different, we have the new special dungeon format coming in 6.25. (Please look forward to it.)