Again, up until Dezolis, the game is not too difficult. Sadly, there's way too much grinding required to be feasible as a speedrun. Lashiec and Dark Force just completely wreck you, even if you're at a solid level and have decent equipment.
Yes, There grinding required obviously, I dont see how that means single segment is "not feasbile". Im guessing a good time would be like 2:30. Is that too long or something? And you say Dark Force 1 requires too much grinding when hes like the easiest boss in the game with Raja, you dont need to do any grinding for him. I think youll probably need about 45 minutes total grinding in the game which isnt too bad. Also I'm positive Zio will be the hardesy boss in the game in an optimized run, except maybe lassic.