"Great throws" into "tight windows" are almost always subject to 2nd guessing. Get picked and it was an "ill judged" decision.
But make it, and you're a great QB. And, you know, today you have to complete balls like that to be successful. Coverage is so damn good these days that, if you settle for safe throws, you ain't goin' far.
The test is not the individual throw. The Kupp throw worked; that pick in the EZ against LAC (was that the game?) didn't. Essentially the same decision.
The test is in a large sample size. Over time, does a QB making aggressive, bold throws into coverage end up with lots of picks or lots of completions?
Goff's stats are pretty damn good. What that tells me is that A] he has a really sharp sense in his vision and judgment about whether the room is really there and B] he is accurate enough to generally make the throws. That is, for him, pulling the trigger is often a smart move whereas it would be a bad call for the average QB.
And that is the definition of an elite QB.