Not sure on its relevancy with the J-20, but about the stealthy thing, we never knows, all these recent few years with the rapid technological progresses all are just one's claims vs the other's claims,,,, the masses never know the real ones...
Or are we really sure that the
major powers cannot detect the aerial stealth things all these late years? Or they just see no advantage to unveil that kind of claims by other major competitor?
And just think what's the real advantage of any
major power to openly & undeniably declare (furnished with hard proofs) that the competitor's stealth is ineffective at the current stage?
Is there any strong justification and benefit?
The aerial stealth things in particular, among the
major powers are
more like a religious faith, the high priests keep on preaching their listeners that their holy books are the most correct ones as well as their God... but we never really know the truth for no involved party is willing to do so... just no net benefits to point out the weakness of the other's perceived major striking force... all are just own claims & statements...
but of course they're still effective against the majority lesser nations
(that's why the imposing looks of the many CSG or those huge truly long-range strategic bombers with nuke strike capabilities pose their own merits regardless their huge total costs... among others they all pose the physical presence that cannot be denied... at the minimum they give the perceived advantage or superiority that's sufficient to keep the many lesser nations in order 
though we don't really know how effective they're among the major powers in today's technological context! Sorry to sidetrack a bit)
land based cruise missile can't reach west coast of USA like Hawaii and Alaska
