If I travel with Mrs Tyke and/or Little Tyke then the railcard discount is available to me too, which then makes your northern examples cheaper than your southern examples. On top of that, the railcard is proportionally cheaper per person and has fewer restrictions. We can play this game all day but the only way you can make a meaningful comparison is to compare apples with apples.
Yes, and no.
Leeds to Newcastle doesn't have a day return, although you can buy a North East Round Robin for £65.20 and use it as an off-peak day return.
Leeds to Carlisle via Appleby does have a day return but it doesn't have an off-peak return. It has an anytime short return instead, priced at £64.70, which compares with the off-peak return from Leeds to Newcastle at £79. But in exchange for your cheaper fare you're restricted to a slow rural branch line where there are only 6-7 trains per day.
The expensive bit remains York to Newcastle, as we all know. And yes, the walk-up fares charged for that journey are eye-watering, no argument from me on that. Thanks LNER.
Even this ends up being swings and roundabouts.
One thing the south east doesn't really have is rovers. Whereas the north has a very good selection of rangers and rovers.
The Leeds to Manchester off-peak day return at £28.40 may or may not be good value. But the South Pennines Day Ranger at £31.20 is, I think, pretty good value.