There could easily be a safety differentiation between the Pfizer drug and the INCY drug precisely because the INCY drug does not hit JAK3.
Inhibiting JAK3 is immunosupressive, and so there could well be fewer serious infections (like reactivating TB) in the INCY trials than in the Pfizer trials.
The INCY drug seems to promote shingles, so it has its own immunosuppressive issues. (It's not straightforward to give the shingles vaccine to this patient population because they are typically already on various immunosuppressants).