I cant speak to shade, never played her, but I can talk a little about slayer and melee in general. Vermintide has always been a mechanically intensive game with a significant skill ceiling as far as combat is involved. In the words of an many a vermintide vet “health is the golden resource” and learning to avoid damage is the main skill you develop as you play.
To that end, the two main ways to keep healthy (besides consumables like health draught) are health stealing talents and combat skills like blocking and dodging. Every character gets life steal at lvl 20 and i think that is why you dont get those more melee focused careers until later, giving you time to develop those skills as you progress.
Slayer can be punishing right when you unlock him, But i belive you can play around these disadvantages. My worry is, if you give extra lifesteal to these classes they will be far too tanky once they are fully leveled or power gamed.
Finally, I really like that the perminant lifesteal from VT1 was replaced with temporary health.
Tldr: Not too fond of more lifesteal, I like where melee oriented careers are, though i wouldnt be against melee classes getting slightly more health in kill or crit.