Raj and Shatabdis are fully A/C trains and powering the coaches will require a generator with a good output. If the HOG's don't have a high enough capacity, then they can't power the rake all by themselves. Also, since these are premium trains, they need to maintain the A/C continuously without any interruptions. That's why EOG's are used. Partly for reliability and mainly because the HOG cannot handle an entire rake by itself. At this point, you really can't avoid EOG's if you want LHB coaches.