Right at the beginning you said you were really happy with the disc conversion for the front brakes. Was you hoping converting the rear brakes would be a similar step change? My advice would be to keep stuff as simple as possible. Changing from drums to discs seemed straightforward and yielded good results but now it seems you are in search of perfection and going down a rabbit hole of complication to find it. If the setup with your existing MC is satisfactory, why complicate matters and spend much time and money on a minor improvement. If the rear brakes didn't feel like they were doing anything before it's not the fault of the new kit, you need to look elsewhere in the system
Yes i personally would leave it as is as i really am happy with it but others have suggested fitting a duel line system which does complicate things but as i'm happy with it as it is i think i will keep it as it is now.