prologos to answer your question ea team has a cap...they can only spend so much for top talent. Actually many of the difference makers were NFL cast offs who were low draft picks and / or undrafted free agents.
Here's what one of the Seahawks scouts said about this 2013-2014 team
"The Seahawks are not just talented. They are mysteriously talented. They are comprised not only of draft-day afterthoughts who have become quality starters but draft-day afterthoughts who have become stars. It is as confounding as it is rare."