Thank you for the question. Hard, sheep, chewings, and tall fescue are all bunch type turf grasses. Red and creeping red fescues spread slowly via runners to help fill in the areas left by the bunching varieties. It does appear that you have bunching fescue growing quite well but I don't know the varieties. You may very well have tall fescue in the mix already and the varieties developed for our area are tough and drought resistant.
Your goal of low/no maintenance is very achievable if you stick with majority fescue grasses because they put down much deeper roots than Kentucky blue grass and are thus able to tolerate drought much better. The downside is that compared to Kentucky blue grass, they are slower growing, slower to green up in the spring, and many bunch which some people consider unsightly.
One of the ways to mitigate the bunching is to mow less frequently or not at all in that area. These grasses only get about 6 inches long and then they softly bend and flow, looking quite lovely. The "flow" helps disguise the bunching until the creeping fescues can fill in. This will also shade the soil to minimize the growth of undesirable plants.
Personally, I think it would be a shame to eradicate the healthy fescue that's in place now. You could check the packaging from your experiment to see what varieties of fescue it contains. If it has a fair percentage of creeping and red fescue, you could try overseeding with this mix because it does look successful in your photo. Often, seed mixtures with a bit of bluegrass are more visually pleasing to people and once established, can be quite tough in a low maintenance situation.
An alternative would be to find seed mix that consists of a majority of the red and creeping red fescues to boost the bare areas. If you do an internet search for No Mow Lawn seed, you will find nurseries that specialize in this and you can order some seed. Some nurseries have great websites that really explain how to plant,care for, and trouble shoot these grasses. We don't promote one source over another.
The University recommends over seeding in August or September because weeds are less actively growing at that time, the new grasses can sprout and establish before winter, and then can get a good start in the spring before weeds get going again.