I don't believe that NFL Teams could structure short term fully guaranteed contracts and maintain the ability to build a sustainable, truly competitive roster, with the way the Salary Cap in the NFL is Structured (Hard Cap) versus the NBA and MLB. Both of those leagues also have smaller rosters compared to the NFL and fewer "Key Positions" that get paid elite money regarding that league's averages. Not to mention players who are either over-valued by teams from the start or those who "lessen up" after getting paid, would just help to magnify each mistake a team makes.
I believe Sherman's Contract is actually a lot closer to a balance between team and player and although not exactly where it should be is close to how contracts should be structured. Sherman is getting paid a few million each year just for being on the team and putting his body on the line, then per game played and per his performance he can make an amount that puts him in the pay bracket that he feels he can perform at. It's nearly a perfect balance of risk/reward between team and player. The only caveat is percentage of playing time which is a far greater risk for the player.
So to answer the 1st question in short, No I don't believe the NFL is behind MLB and the NBA when it comes to contracts being guaranteed, but I do believe the NFL's contract structure is becoming, if not already, outdated.
* I want to add I believe if the NFL is going to adopt something from the NBA it should be something similar to "the max contract for homegrown talent" and even just max contract structures for players with certain accomplishments. Maybe teams could give their 1st round QB a max contract that pays him in the top of the league on average and maybe max contracts give a discount for teams on the salary cap for an example. This would allow players to be rewarded for good play and teams to be rewarded for drafting and developing talent, while also allowing teams to keep their talent and creating more competition throughout the league.
[ Edited by NinerLegionnaire on Mar 13, 2018 at 1:57 PM ]