Could the drain be raised or a different taller drain cover so the tile butts up against it like in your inspo pic?

" the tiler did use Redguard for waterproofing "

What was the substrate the applied the Redguard to? What about the pan?

It is unfortunate, but homeowners need to be knowledgeable in today's world re: renovations. Luckily, I had just started reading Houzz posts about six months prior to my first bathroom renovation. Due to all of the comments asking about waterproofing (on posts that had nothing to do with waterproofing), I realized that it had become a big issue.

I also learned the steps required for a traditional water in - water out custom made shower pan + how many contractors would skip the required pre-slope UNDER the vinyl waterproof liner in addition to the slope made on the liner (the liner would be installed flat on the subfloor). I was able to immediately spot an issue when my contractor failed to install a pre-slope under the vinyl liner. I also took MANY photos along the way to document the construction of the shower.

I would ask how the shower was waterproofed. You could do it in a way that is not accusatory - maybe tell him/her that you are asking for a friend who is going to DIY his/her shower renovation. You could simply say that your friend asked you how your shower was constructed - and that you said that you would ask your contractor because you weren't sure.

If you simply ask about your shower - your contractor may assume that you believe that it was done incorrectly = you may not receive an honest answer. You still may not receive an honest answer, but at least if you pose the question similar to how I have suggested, he/she won't be defensive and there is a chance that he/she will provide the steps that were used.

There are many contractors who believe that the way they are constructing showers is a perfectly acceptable option - even though it isn't. There are "how-to" videos on YouTube that show unacceptable shower construction methods. Obviously, the creators of those videos honestly believed that he/she was providing helpful information for DIYers.

If you’re careful with your finish selections, you can make the old tub work. It would be a shame to get rid of a good tub.