MythTV's design choice requiring version sync across all clients/backend does indeed turn out to have been an unhelpful one, but I guess that wasn't obvious when they started.
There are other PVR backends are there not? Such as 'DVR' and I see 'TVHeadend' on the myth wiki. I've not tried either of these but they are probably easier to configure than mythtv :-) The backend when doing digital recording from USB is pretty simple: select channel and record stream at specified time, keep and expose a list, optionally run transcode and ad-remove processes. It's rather more fiddly with analogue TV cards. Most of the hard bit (UI, display technologies) seems to me to be in the front end. Hmm. I suppose the EPG database has to be in the back-end if delivered over the air. That complicates matters.