Nothing to add to your great post except the NFL is also an acronym for not for long.
A position of strength can become a position of need very quickly for the reasons you stated.
But the teams that draft strictly for "perceived need" are typically the ones that are perennial losers....like teams that continue to miss and draft QB's with early picks a few years apart....or teams that reach for a player just because they play a specific position.....I like the Saints draft philosophy with accentuated the RAS numbers, still, it doesn't always work out.....I think, as with many things in the NFL, luck is a much bigger factor than anything else.....injuries have shorted what should have been a lot of good careers....