You're taking his game intelligence for granted.
Players with ridiculous amount of natural talent, such as Gerrard, have failed in that position. Players with little talent, such as Spearing, have been shite in that position.
Top teams are always on the lookout for players in that position for a reason.
There aren't that many that can excell in that position.
Comparing him to Suarez isn't really fair.
But is he easier to replace than the rest of the squad? I think the answer's a big capital NO.
I think there are more players in the starting 11 that would be more costly to replace than a DM like lucas. I rate him and all that, and having someone in that role is very important to the team, I just think it's a very basic and simple job, which he does well.