In a one-coat floated install, the cleavage membrane (roofing felt in this case) is the old-school method of waterproofing. There are installers who will waterproof membrane over that for peace-of-mind, but like you mentioned, there's some disagreement about whether that traps moisture or not.

That said, the paper tape and drywall compound is a no-no. In fact, if they are floating, there's no need to tape the seams, so I'm not sure what's going on there.

Plywood, joint compound, and paper tape, do not belong anywhere in a shower. Hot mop is antique technology. If he can’t get the rest right, he probably hasn’t done any of the rest correctly either.

pay close attention to how they attach Lath to the STUDS THRU the dens shield. Recently saw a clown try to staple lath to the dens shield NO NO !

EXP1 plywood is fine for aquabar/felt/lath *IF ITS DONE RIGHT

i dont like gypsum mud taped corners , theyll present possible issues over leaving them untaped as will the gypsum inside the denshield by the time they staple tru it and the felt/paper.

In cali you are at the mercy of outdated methods and inspectors, what did the inspector say about the Preslope and the flood test? did they not want to see the lath work as well?

All that being said There are some of the BEST tilers still floating walls and hot mopping like it or not.

Many thanks Mint Tile. How should they attach the lath to the studs, if they ask why not staple?

Also do you recommend putting a couple of coats of AquaDefense over the exposed plywood and seams in the niche?

Usually we use protecto wrap or similar flashing in the niche when floating.. Stapling lath to studs is mandatory not short staples into dens shield.