personally, I’d do these changes very differently, I would personally mix the 20/26 together, having the 20 do the normal route, then head into Oakwood & back via the 26 route, the same in reverse with the 26.
The 20/21 situation is good in the fact Spondon is getting a bus service again, I do believe some park & ride services in Derby should be introduced, I remember the D1 between Derby & Meteor centre running for years, as ‘trainman’ said having a service to kingsway would be handy.
But again, I’m glad to see Arriva extended the network, while timetables & stuff may not be perfect it’s a basis to work from.