Nice job! Mixed tanks are always nice.
One a side not, have you considered a slaying sphere build with QR in b-slot and Heavy Blade as the seal? He has the attack to pull it off quite reliably, maybe threaten atk in C-slot?
I actually haven't considered Slaying Spear. I wanted to make him more of a reliable mixed tank, which is why I went with Berkut's Lance, but I'll test out your suggestions and see where that leads me.
That’s one heck of a Donny you got there. Once he hits the max merge, you’d probably be able to slap a skill like sol on him and solo maps without breaking a sweat.