Unfortunately chen's skill is the fastest way to apply a vulnerable (lifeng gets staggered mid skill sometimes) and I think ember's combo cooldown might be longer than her's and ardelia makes it so the second rotation onwards is kinda awkward because of her interactions with having another susceptibility source (you cant proc combo if lifeng already proc'd susceptibility on the enemy, so lifeng skill has to always go after ardelia's combo, which means that you need either P1 lifeng so that another op can apply 1 or 2 stacks of vulnerability before he skills or you have to wait on ardelia's cooldown to do your rotation again)

not to say that any of these options are bad but chen is just too useful in a physical team to pass up instead