I also think that an 800mm shower is small for washing a dog. We fitted a 900mm one at a previous house and found it really tight for showering our mini poodle sized labradoodle. We rarely used it.
Otoh, I'm not a fan of wet rooms either, but that might just be because they remind me of the one my parents had, which - whilst fitted with expensive sanitary ware and furniture - always felt very care home-y to me 🙁
The 900mm shower was in a five bed house where we had a family bathroom and a separate shower room upstairs. In addition, near to the kitchen we had a fairly spacious loo-tility with washing machine, butler sink unit, floor-standing boiler and loo.
The reason we put in the ground floor shower room was because a previous owner had built an attached annex which we incorporated into the main house and it was some distance from the other loos in the property - plus we were a) thinking one of our parents might move in and use the old annex as a bedroom, so a shower room next to it would be useful and b) with an eye to resale - it might be used as sleeping quarters for a disabled relative etc.
At the house we owned prior to that, there were two bathrooms (one actually a tiny shower room) on the ground floor when we purchased. That property was bottom heavy, with two beds (no bathroom) upstairs and five reception rooms, a conservatory, kitchen and the two bath/shower rooms on the ground floor.
We put in an ensuite bathroom to the main bedroom (upstairs) and converted the ground floor bathroom to a second shower room because it was quite a small space. When we sold our buyers had five DC so intended using several of the ground floor rooms as bedrooms. The two downstairs shower rooms worked well for them.
We're in a much smaller property now and there's only two of us - plus two dogs - at home. We're currently reconfiguring the ground floor which involves extending as well as putting in a cloakroom. We considered adding a ground floor shower room - again mainly from a resale perspective - but decided that it wouldn't make the property (a small, 400 year old mill that currently only has two beds and one bathroom) any more saleable. If we decide to go up into the attic, we'll put one there instead. There are so many steps involved in the approach to this house, it's unlikely that an elderly or disabled person would buy it anyway 🙄