TL;DR: fractal releases are seeing useless and poorly explained mechanics for the sake of keeping "story". To resolve this, plan future fractals around progressive mechanic design as well as make Dessa say more things about mechanics
Currently, there is a common pattern among the recent releases in fractals in which I would name "mechanic bloat". This bloat often reduces what would be a interesting and arguably fun fractal into a thing that the average player would avoid playing when it comes up as a daily. This is increasingly becoming more of a problem as more fractals are being released and should be drawn to attention to for future fractal releases.
What is mechanic bloat in my context? This refers to the addition of irrelevant and contextless mechanics within a fractal that does not develop for future fights or is poorly explained when it is introduced. Using Siren's Reef as an example, there are two main examples: Blasting Black Pete and Captain Crowe's Grim Lagoon (red AoE) and Teeth of the Deep (green AoE) attacks.
Blasting Black Pete, in all honesty, is a useless boss. If this boss was removed right now, a new palyer would not find anything harder to learn than now since this boss does not have any impact in how the fractal progresses. It does not provide a mechanic that one would take to a future fight and does not even help in explaining ANY mechanic in the fractal. There are so many useless mechanics that does not get carried to future fights. A player can destroy mines with cannon fire, but outside of that fight when do you use that knowledge? What other mechanics does he have? An example of an arguably good mechanic design is the minotaur boss in Deepstone. It teaches players to use the Special Action key to "reveal" it to make it vulnerable to damage, which translates to "revealing" tiles in the maze, and then to the final boss in which you reveal lost tiles in the battle.
Captain Crowe's two main pug killers are really not explained at all. People still do not know that the Grim Lagoon (the red AoE) does NOT damage trash mobs like a flux bomb does, but instead gives them quickness and protection. Similarly, some people do not know that the Teeth of the Deep attack (the green AoE) is shared between the players inside with 5 players being almost 0% damage. These mechanics are not explained due to the assumption that players are familar with "raid-like" mechanics of red being bad and green meaning share. This negates the idea of fractals being a "precursor" to raids as it would assume that you would know that fact beforehand.
In order to prevent this from repeating in future releases, a fractal needs to focus not only on story but on cohesive mechanic progression. Using Siren's Reef as an example again, I would have proposed these changes in order to reduce mechanic bloat as well as make it easier to explain mechanics: the introduction of a second path similar to Aquatic Ruins and Underground Facility, and more dialogue on Dessa's part in explaining the mechanics.
I would introduce a "First Mate Shane" NPC that would lead the original path of the fractal right now and introduce a new diverging path in which the fractal team follows Weyandt and Captain Strohm. First Mate Shane acts as a leader to follow in this fractal as well round off the narrative, Strohm telling Shane to take the rest of the crew and find a ship as well as makes Weyandt's story on Strohm giving him "leadership" act more believable as he has to convince the second in command. In the original path, I would introduce a red bomb AoE attack on Blasting Black Pete that acts similar to Sabetha bombs while giving the trash protection when it detonates. This can then be followed by Dessa saying something like "It seems the excess ectoplasmic discharge from this skeleton is empowering the other ghosts, don't let those explosions touch them!" to warn new players that red equals bad.
In the Weyandt path, the first boss would be a ghost that controls sharks, in which does a lesser version of the Teeth of the Deep attack and makes Dessa say something like "Those sharks may seem real, but its an illusion created to single out your allies to pick them off, try grouping together instead!" teaching players that green is good. Then you can do a segment after this in which Weyandt sends you off to collect something or to disable blowing winds while he feeds Strohm the poison and then when you come back Weyandt escorts you to the ship and the normal ship part starts. These changes all include progression of mechanics that you would eventually see as well as reinforce the idea of certain mechanics.
With this said, the future of fractal development should also focus on a cohesive mechanic progression to prevent players from avoiding potentially fun fractals in the future. Fractals should actively state what is good and what is bad from the get go instead of assuming that these players have knowledge. Futhermore, mechanics should be developed through the progression of the fractal as to make it more fun to learn mechanics leading to the final boss.