A couple of issues have already been addressed. If the subfloor was inadequate, it should have been beefed up prior to setting the Kerdi base. Other than that, it's pretty much installer error. The Kerdi system is pretty much bullet-proof if you follow the instructions. If the base is flexing, it's due to an inadequate subfloor, an improperly set base (no thinset, wrong thinset), if the membrane isn't adhering to the sloped top of the tray again it's installer error (wrong thinset, operator error, etc). Do you know what specific adhesive they used to adhere the membrane to the base, and what specific adhesive they used to adhere the tile to the membrane? Mastic? Thinset? Premixed or powdered? Modified or non-modified? Brand name? I highly recommend calling Schluter's tech line. They're very helpful and if it's a Schluter problem, they're quite willing to fall on the sword and accept responsibility. Even when it's installer error they help out. Mongo

I used a Schluter system for a shower build a couple of years ago. It was very easy to use, but I spent a LOT of time studying the Schluter videos and followed the directions precisely. I also planned the shower very carefully to know exactly which corners and other accessories I would need. You may need more interior or exterior corners than are provided in a "kit", depending on your shower design. Be meticulous in preparation (studying all the videos and documentation, prepping the wall, etc.) and application of the membrane. I also used the Schluter drain and it was very easy to install. Good luck on your project.

We used it for a corner "foot bench". It's not very big, but it seems very sturdy. I would feel confident standing on it without it crashing to the ground. You should still use the Schulter waterproofing material (i can't remember it's name) to wrap it.

The profile is not even resting on tile properly in the #3 pic regardless who bought it A few hiring tips for anyone reading , Always ask the prospective tiler whos going to install, is it you yourself or do you send in the B team , the C team etc. Secondly you will know when you have a tile pro in your home, they will start getting less and less interested when you start declining having them order purchase and supply every last bit of tile related material for the project its not always about profiting or markup but more about risk and having a smooth project , this also puts the liability in your favor when things backfire vs attempting to shave a cost. One must ask themselves if they know enough about the tile business to be qualified to guage the prospective hires "knowledge"as well as select and purchase the correct materials . There is so many new products, methods , industry standards and a million hacks out there coming in with low rates willing to engage in sharing liability be very careful in the hiring process. @OP youve got the C team and i think the B team is on vacation here