Nice take on it. I think the Left Tackle position in particular has become the second most important position on the field, protecting the QBs blindside. It's amazing what Mailata has become and I'm incredibly proud as an Aussie-Samoan.
But pass rushing, cornerback play, and receiver production
If I had to pick between the three, I'd say cornerback play. A good cornerback can limit a quarterback who has ample time because of a substandard pass rush. It also keeps the score down so helps stop scoreboard pressure which can result in a QB throwing errant passes.
Cornerbacks are one of the best paid positions too which I think shows the value of a CB.
I might agree with you here, you know. Despite EDGE tending to be the most valued defensive position, I personally love having an elite CB, to the point that I might take that over an elite rusher depending on the team's makeup. Sauce's effect on that Jets D is an obvious example, but prime Darrelle Revis was one of the most valuable defensive players I've ever seen. I also don't quite understand the importance placed on receiver, despite the fact they're obviously valued heavily. There are tons of good receivers, and a great QB can elevate receiving talent. Would rather have a good O-line than receivers personally, though O-line injuries are awful and seem to happen to every team except the Chiefs.
LT is certainly the premium position on the line, and for one position on it, you've gotta go LT as the pick. They just have too much value in their blindside protection. That being said, I would personally rather have a pair of good guards and a pair of good tackles- cheaper, better for the run game, and imo interior pressure is more devastating than edge pressure for overall QB production. I reckon it'd be easier to get a great IOL and have passable tackles than vice versa, and I think it'd have a greater effect.
What I've noticed in many good O-lines at least this season is they tend to have at least one good tackle, and often two, and then a good center and one good guard, with another guard not being as good. It seems that in reality, guard is the most replaceable position in terms of production if the rest of the line is good. This also explains the value of the tackle in terms of both draft position and contract spend.