Regd this. I just downloaded very old Sitcom, i.e., Malcom in the Middle. The FHD episodes only required 320-330 mb ie., if its a 40 episodes its almost equal to 650-700 mb.
And Regd your claim that Netflix uses very low on Mobile. Here's my experience with the same. Mine is L3 certified so its SD max on Netflix ( which is not a problem on Hotstar or even Voot now) for SD alone for Friends episodes it took like 250mb each. I haven't tested FHD as I wont get them. Hotstar's Video player has improved a lot in last 1 year or so.
Ps. Sometimes on Samsung QLED TV(which Hotstar hasn't updated yet) I feel Hotstar's service better than Prime Video (No problem on Netflix). Even today I had watched The Personal History of David Copperfield without any pixelation or what's so ever on Hotstar, but Jaati Ratnalu ON Prime pixelated so many times (I had tested on Speed Test speed was around 8-10 Mbps consistently) for that FHD video it's more than enough imo. I agree Hotstar has a long way to go to get better performance but saying almost everything isn't proper isn't good imo.
As a matter of Fact HOTSTAR now supports even HEVC as well. This is from one of the Episodes I had downloaded.
{"Device Name":"COR-AL00","Buffer Time":"2.5 s","Screen Resolution":"1080 * 2128","Video Resolution":"1920 * 1080 @-1.0 fps","Video Id":1000114253,"Video format":"video\/hevc \/ hvc1.1.6.L120.90 @132.0 kbps","Audio format":"audio\/mp4a-latm @$48.0 kHz","Dropped frames":"0","Network speed":"0 KB ps","Buffer count":"18.0 s"}