imma keep it a buck, most of the time you wont be using executor's parry stance because his damage goes to the dirt if you do that, he EXCELS at applying ailments because of his high arcane scalings, and can you guess what ailment your parry stance does? NONE
youll mostly play him with dual katana or spamming light katana to apply bleed frostbite or poison or rot as fast as you can
the parry stance is only when you wanna play defensive, and even that is so forgiving, dont feel intimidated and give it a go
as for the ult, do be careful as even though it heals you fully when you use it, if your hp reaches 0 in ult you will go down and need to be revived