While 18424 competes with PFE's directly, I think for disease like RA with big and diverse market, no significant differentiation is not major burden, as you can see from antiTNF agents, which are all big sellers.
INCY claims non-inhibition of JAK3 affords differentiation relative to PFE, but it remains to be seen if this is a consequential distinction.
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”