"And I’m not sure this is even a real problem." The membrane will provide waterproofing. The caulk and grout? For the moist part, they are there to help the surfaces shed water and to help maintain sanitary surfaces. You've gotten some good answers. Changes in plane are typically caulked. Caulk is flexible and can move when adjacent surfaces move independently of one another. Grout is rigid and can crack. Cracks in grout can be from movement...typically in corners, from differential movement...or because too much water was used in the grout mix or during clean up. Cracks in caulk are usually shrinkage cracks. Not enough caulk was injected in the crack for the caulk to properly bond to the adjacent surfaces...Or too much caulk was injected in a deep crevice, and as the too-deep mass of caulk cured and shrank, the shrinkage forces were strong enough to break the bond between the caulk and the edge of the tile, or they caused the caulk to crack right in the middle of the bead itself. For deep gaps that need to be caulked, a foam rope (backer rod) is inserted into the gap to reduce the depth of the gap. That allows the caulk to be injected in the gap at the proper width-to-depth ratio. Caulk texture? There both color- and texture-matched caulks these days. So if you have sanded grout, you can use a sanded caulk to help maintain joint texture between grout and caulk. Unsanded grout, use regular caulk. Repairs? In general, it's not wise to shmear a thin veneer of caulk over cracked grout. It's better to cut the grout away as best as you can and then properly fill the gap with color- and texture-matching caulk. With a Schluter shower, great care needs to be taken in cutting grout out of the joints. Go too deep and you can violate the integrity of the membrane. Your wall corners will have membrane behind them, with the membrane bridging from one wall to the other. In a non-steam shower, there is a chance that your wall-to-ceiling joints do not. Depends on the habits of the builder. The sooner the repairs are made the better. Grout hardness, ease of color-matching, etc. Good luck with your repairs.

IMO the floors should be the same and your inspiration pic has a very simple stacked wall tile with that floor and that is what I would have done in your shower too I think the 2 patterns will compete with eachother and the dark grout on the walls will make it even more so

Support your local independent tile store! They usually carry a wide selection for all budgets. Look on Houzz and you will find plenty of photos of bathrooms using the same model tile for all surfaces, but in different sizes and finishes ... matte for floors and polished for walls.

It seems every bad tiling post has a comment from the contractor along these lines when the work is questioned, "this is all okay and I have been doing bathrooms for 30 years." Yeah, doing it badly for 30 years and leaving mold in your wake. The next comment from him will be, "I've never had a call back to fix it." Yeah, because no one wants you back in the house when you screwed up the first time! Honestly, this is the issue with home improvement, you can't rely on people to do what is correct, you have to learn the terminology, the requirements for proper install, etc. Otherwise, how would you know if it's completed correctly? We pay a professional because we don't know how to do it, but we end up having to learn anyway. Good luck, OP.