First of all, I will give you credit for space utilization by placing the shower under the stairway. It was probably the best spot to put it in considering the layout of the bathroom.
Next, let’s talk about the cider block walls you used to enclose the space. Two of the three are reasonably square and plumb. That third one though? The top leans two inches into the shower as opposed to the bottom. That probably accounted for how peculiar those brick columns on either side of the shower entry look.
And since I’ve brought up the brick columns? Why? My first thought early on was perhaps they were load bearing as the main floor tub is right above, but no. The are just “decorative” for a very strained meaning of the word “decorative”. Fortunately, you were a poor mason and they have come down rather easily.
And as they came down, it helped take down the plastic shower surround, which I knew was going to hide some things. Above the surround was a decent tile job (even taking into account the non plumb wall) I assumed some cracked or missing tiles and I was not disappointed. From four foot down, it looked like most of the tiles weren’t there once the surround was ripped out. Finding the tiles had been adhered to plain old, paper-both-sides sheet rock was a little surprising, but to top it off by replacing the missing tiles and sheet rock with 1x2" and 1/4" plywood was a true sign of your DI-WHY “creativity”
Oh and I almost forgot. Cementing in the shower fixtures, really just makes me unhappy. When I realized that the copper pipe for hot and cold go into a cement patch on one side and the hot and cold taps are just as firmly encased on the other side, I knew serviceability was nowhere in your thought process.
Sincerely and with some malice,