Well, even with my well honed and lithe body (who you kidding?) I always start the bike on the stand, just using most of my weight rather than a leg kick. Always done it that way, and always with a pair of decent footwear.
But this conundrum could stem from tappet and ignition settings being initially incorrect but not far enough out to prevent running. Putting one right and it all goes to pot. If I've read it right there is no resistance to indicate internal binding eg coil bound springs etc with the plugs out. Oil in the bores could be another cause, but as the motor is now running, oily exhaust smoke would be a clue to a problem here.
Reckon it's back to basics, time before TDC and drive the timing gears via the crank to eliminate backlash as the piston rises to the static timing mark, stick down the hole method. Auto unit must be set at full advance, wooden wedge trick.
Swarfy