Worth saying that there isn't much commercial stuff left in Cheshire East though. In part due to persistent failings over many years by both operators and the council.
The bulk of the commercial services are in and around Crewe (8, 12, 31, 37, 38, 84, 84X, 85 and 103). I believe the only other CEC services that are commercial are the 3, 10, 14, 19/19A (Upton Priary section only) and 58 in Macclesfield plus the 42C (serves Handforth Dean only) and 199 (Disley).
Profitable is probably a bad word for it. More it will lose less money than the 19. If the 85 can be gotten down to

0 minutes each way on Sundays to get a nice hourly service with 1 bus. I agree though it could be slightly better than a 19.
Perhaps but 35 minutes allows for 1 bus to operate every 90 minutes, which if on opposite times to 84 on a Sunday could allow a regular 45-minute service between Crewe and Nantwich
42 I don't think would be the best thing for Middlewich, I'd do the 37 same as Sundays. 1 bus Winsford-Middlewich which ideally links into the 38 (as this is something that the 37 has done for years on the short trips to maintain connections). The 42 would be 2 buses and it plods around areas that don't tend to use the bus much anyway. Least the 37 is, as you kind of suggested earlier, putting a Sunday service on an largely commercial route.
This was more if South Cheshire only had 1 Sunday addition with BSIP, the 42 would serve Frank Webb Avenue/Rolls Avenue, which is a dense part of Crewe which the 85 does, allows Leighton to see more buses which is a strategic goal and connects to Middlewich only, largest town without a rail service in CEC. A 2-hourly could then operate including driver breaks if did Crewe - Middlewich only
Nevertheless, there are parts of the network in Crewe which would be better value for money than additional Sunday buses due to larger patronage, lower car use and higher density. An example would be increasing the support on the 84 corridor to allow an hourly bus service to return which would probably be more successful given this route has 4 buses an hour Monday-Saturday so 2 every 3 hours is a huge drop on Sundays