-atk +spd M!Morgan

His attack is already on the low end, so this will hurt him, however, I'd say he is still useable. Grima's Truth is a great tome and will boost his attack and speed a fair amount. You'll probably want something like Fury/Darting Blow/Swift Sparrow for his A, though Steady Stance and Close Counter are both really useful on him as well. Windsweep is a great B, allowing him to safely buff allies and debuff enemies. With the proper A skill, Desperation isn't a bad pick, either. Vantage is always a great option. Morgan might make great use of a Drive ability for his C, as units will need to be in that range to receive his buffs. For his Seal, I'd argue Close Defense. This will allow him to be very tanky after landing his debuff. With enough speed to prevent being doubled, he can sit comfortably at a 41 defense on Enemy Phase after applying his debuff.