Part of the problem is speed. I had this issue with a tough starting 40 hp outboard. The engine started better by pull starting it than it did with the electric starter. My engine guy tells me, it is because when you use the pull starter, you spin the engine a lot faster for those one or two revolutions than happens with the electric starter.

That might have to do with Magneto strength as speed increases and may not be relevant to Diesel, but there it is. On the other hand, if your electric drill can spin the engine at the same speed the starter can, why not?