Road conditions on your first route
Isb to Balkassar - Motorway
Balkassar to Mianwali - Single but fine and wide enough less the Musakhel-Mianwali section which is broken with potholes
Mianwali to kundian more - Broken and under construction with diversions intial about 7 kms, later fine
Kundian more to chashma - Single, narrow with potholes
Chashma to DI Khan - Under construction with frequent diversions
DI Khan to DG Khan - Partly fine but mostly broken due to heavy traffic
DG Khan to Rajanpur - Same as above
You may like to consider the following 3rd option
From Mianwali take the MM road to Muzaffargarh, cross over indus to DG Khan and then Rajanpur.
This would save you distance and also keep travelling on the east of indus within Punjab with relatively better road conditions.