Yep, Earl Thomas was the linchpin to the entire LOB secondary, without Thomas there is no LOB.
Earl Thomas was a fast, rangy safety with killer instincts. His skillset and athleticism allowed the LOB to play an aggressive style of football with virtually no drawback. Squaring up right in receivers face and aggressively pressing them at the LOB, especially with bigger, slower DB's like Kam and Browner couldn't happen without Thomas in the backfield. Chancellor in particular was able to function almost as a 4th linebacker at the LOS due to Thomas's instincts and range.
Even if one of our DB's whiffed when they tried pressing people at the LOS, Thomas would be there over the top to break up the pass. I surmise this is why Browner could stick on an NFL roster and struggled after he left the Seahawks. He was a bigger, slower DB with stiff hips -- which is why he ended up in the CFL before we signed him. What he was though is physical and adept at mauling receivers at the LOS and getting away with it. I don't think he would have worked well with most NFL teams.