Seigan is barely a single potency-per-kenki higher, than Shinten and yet it will separate parses, too. In group play, Guren's benefit also has a lot to do with how quickly all that damage can be dealt. You can fit that 800 potency into a single 5-stack-Embolden, Trick Attack, Battle Voice, Brotherhood/Hypercharge, Chain Stratagem, etc., more easily than 2 Shinten alongside the Kaiten, Hagakure, MKSS, etc. of your opening burst.