He's definitely got the right attitude but we haven't seen him play against anyone in the top 10 outside of Tipsy, correct?
He's played Nadal twice and lost in straights both times not even managing to get one set to a breaker (Tokyo 2010 and 2011). I agree he's a better player now then he was even 6 months ago but it's not as easy to get to a tie breaker against Nole/Rafa/Andy etc. as it might be against someone like Istomin. Those guys will get some of his serves back and even if it's only one serve every game at a certain point it'll mess with his rhythm knowing that not every ball will be an ace or an unreturnable..
I'm sure he'll beat them at some point - Karlovic beat Roger, Dodig beat Nadal etc. and Raonic is a far better player than either of them - but that doesn't equate to saying the gap is not big. The gap is huge - in terms of experience, titles, skills (movement, FH, BH, ROS, volleys, defence, mental strength - pretty much everything but the serve). Good for him for being positive but the reality is that the top 4 are way above the field for a reason - it's not a fluke - they're just fundamentally more complete and consistent than the rest of the tour.