And what does 'in general' mean? Their peak level? Their achievements? Average level in their careers? Since they become top10? top5? In Slams? Slams and Masters? Against the top4? Against top10?
When you compare Delpo and Ferrer (since we all know that's what you are doing), we know few things for sure. Delpo has a higher peak level and is more talented. Ferrer is a harder worker. They are both MM kings and you don't see them often not winning a tournament where they are #1 seeds. And also, Delpo's 'average' goes up and down, but Ferrer's average is steady. Ferrer is never in form or out of form. Even when he 'is' the difference in his level is much smaller than the difference in Delpo's level that he tends to show. Delpo is a bigger threat to the very top guys because of that. You never know if he's going to have a good or a bad match, while you know what Ferrer beings to the table and it's almost never enough to beat a top4 player (bar Murray on clay).
You define me what you mean by 'better player in general' and I'll tell you.
Just in general. Who is more likely to take down the players at the top (Djokovic, Federer, Nadal...) and really shake things up? I agree that Ferrer is more 'consistent', mostly (actually only) due to JMDP's inability to stay healthy/fit for prolonged periods. But as you admitted in your first post here indirectly, not only is JMDP the fifth best player in the world, in the rare occasions where he does manage to stay healthy for a relatively long period he can mix it up with the top 4 on even terms, as his 5-5 record in the past 10 matches against them shows (and not all of these matches were played during such periods anyway). He's the only one who can beat all of Federer, Nadal, Djokovic... without it being a major upset.
This is what I mean with better player; all of the top players are very wary of the threat Del Potro represents regardless of his form or anything else, he's someone who can really shake things up far more than anyone below the top 4. Despite struggling with his health all the time, he has shown that at his best he can mix it up with the top 4 and split wins with them, which no one else really has - that makes him the fifth best player in the world.