I’m sure I would have done edits here! I’ve been visiting this part of Wales every year on holiday for the best part of 50 years - since my parents took us here as kids. I visit the McDonalds there frequently and once spent 4 hours stranded in the car park there with 3 kids after crashing my car at the roundabout!
I don’t think the changes you’ve made to road types are going make any difference. 
The problem is that there are no alternate routes.
Putting a “spine” of normal street into an area like this is only useful if there are multiple ways to reach a destination. As an example, look at this Savacentre and retail park. At the south end of the site is the Sainsbury’s petrol station. At the north is Spine Road and a retail park. On the NW corner you have a couple of residential blocks.
If the segments were all PLR, then Waze would be happy to route visitors to the retail park in from the south entrance and right through the Sainsbury’s car park; same thing for visitors to the residential blocks. Similarly, visitors for the petrol station could be routed in from the NW corner and through the Sainsbury’s car park. Having the sections of street makes sure that visitors get routed in by the most appropriate entrance to the site.
Back to the Carmarthen site, there are no such alternate routes. You can’t get to Dominos by going through the KFC car park, or vice versa. The changes to road type won’t affect the routes that are given as far as I can see.
The only problem I can see is the destinations for the 4 businesses including Dominos. None of them have destination points set, so the destinations will be on the closest segment to the places - and we wouldn’t normally do that. In a busy car park, if Waze directs you to the point in front of a store, the chances are that you will be unable to park there. Meanwhile, you’ve just driven past multiple parking spaces in a busy/stressful environment, with Waze giving you instructions.
Our standard procedure is to add a destination point to places like this - and then place that point at the main entrance to the car park. That way, Waze tells you to turn into the car park - and then shuts up (!) and lets you find a parking spot on your own. 
The Dominos place was locked (because it was previously on promotion), so I’ve added a destination point for that. You might want to set points for the other 3 places. As for the street segments, I think you might as well change them back to PLR.