The fact of the matter is this.
EVERYONE is trying to level Rogue/Ninja. It's new, there's a lot of hype, and a lot of people are flooding low level areas with ONLY ninjas.
The vast majority of Tank/Healer folks are already at 50 and have absolutely no reason to run low level content.
So, to put numbers to it, let's say there are about 1000 players trying to level Rogue/Ninja at once. At the same time, 10 are leveling tanks and 15 are leveling healers. Because a party construction in DF for a dungeon must be 1 tank, 1 healer, and 2 DPS, that means that only about 20 Rogues will get into Sastasha at a time while the other 980 have to wait their turn. It's not a software or hardware issue, it's the same issue that's been prevalent in the game since launch: Too many people would rather play DPS than Tank/Healer.
I play Warrior. I am proud to play Warrior. And by playing Warrior, my queues pop 100 times faster than they do when I choose to play Monk, which is also a job I love to play. That's because of the ratio of tanks to healers to DPS.
If you want things to pop faster, play a Tank/Healer or find a Tank/Healer to join you. Otherwise, you will have to wait your turn. Just remember that DF timers are about 90% reliant on the players queued, and if there aren't enough tanks and healers to go around, there's a good chance you're not getting in.
This same exact thing happened at the launch of 2.0. Because Arcanist was not a class option in 1.X, all the Legacy players were all like "ZOMG ARCANIST ZERG" across the whole field. The only reason the issue wasn't as visible as it is now was because, along with 2.0 came a flood of new players who wanted to play different classes, and thus there was enough variety for DF to work. But here, it's just a ton of people running Rogues and no one's willing to play Gladiator, Marauder, or Conjurer JUST to get through story content.
I mean, I get it. I want to level Rogue to 50 too. But when I see a swarm of, like, a hundred rogues fate farming outside of Aleport, I know that either I have to compete with ALL OF THAT, or I wait until the rush is over. Which could take as long as 2.5, but I'm a patient man.