I'm 5 frags short of getting 8 Gates Lee but I would still use my 4 star Lee because Lee has a resurrect skill, making him a bit balanced when it comes to offense and defense while 8 Gates Lee is focused more on offense and less on defense thus forcing you to put a tank or clone/s in front of him.
you can collect his fragments by clearing survival trial and redeeming frags in collect interface with battle points