I read this and the first question I had was how many pressured the top 5 tackles in the league had last year. It is one thing to say Kalil went form #32 to # 18 and be upset because he is not #1. OK.
But I think they said he allowed something like 33 pressures last year and was #18. If #5 is 5 pressures, then sure, there is a big difference number, but how big of a difference is that really? But what if it is 20 pressures? I did some digging and around and it looks like a solid pressure rate was something like 1.8%-2.5% amongst top tackles. (% of Snaps where a pressure is allowed.)
So lets nerd it up a bit:
I pulled the Vikings and in 2015 they had 973 offensive plays, so if Kalil allowed 33 pressures, that is a rate of 3.392%. So not elite, but to get in the elite group you are talking about an improve 0.9%-1.6%. The mid-point of that range is 1.25%, so if Kalil improved his % by that mid-point he would be at an elite rate of 2.14%. In terms of pressures that drop him down to just 21 pressures allowed.
I hope everyone pays attention to this next part: That would mean Kalil would have to allow 12 fewer pressures THE ENTIRE SEASON. So the difference between #18 and top 5 in the league in terms of pressures allowed is 0.75 pressures PER GAME.
Of course, I'm not sure of the methodology. Is it against passing snaps only? If that is the case then the disparity is greater. The vikings had 294 passing snaps, so 33 pressures equal a rate of 11.22%. 5x greater than the league leaders at 2.5%. Seems terrible right? To get to 2.5% would mean a drop to 8 pressures or a difference of 25 pressures. Even, though the % is much higher due to the smaller denominator you are talking about 1.56 fewer pressures per game over the course of the regular season. So while larger than above in terms of percentage, the difference is literally 1-2 plays a game.
Obviously there is more to it than pressures allowed, but as you can see, when you dig into the stats the difference between #18 and #5 is something, but is it huge? I'm not so sure.
To me, Spielman is in part paid to make decision on what those 1-2 plays per game are worth relative to the rest of the team and the salary cap. How much cap space would it cost to eliminate those 1-2 pressures per game? Is that a good use of the cap space? How much should the Vikings pay in the 2016 market to eliminate 1.56 pressures per game? Another question is can they eliminate more pressures for less by spending on a Guard as the incremental cap or roster cost might be lower vs. eliminating those presses from the left side.

version: I still think Guard gets more bang for the buck.