I think looking back at 2003-2006, it makes quite a lot of sense to rate Raikkonen is top 3 together with M.Schumacher and Alonso. Though retrospectively I have questioned a bit, whether it would be fair to rate him quite on level with them. Maybe a very close 3rd. Then again depends, which exact period or year we are talking about, as Alonso had a scruffy 2004 too, and Michael was older and had started making some mistakes already.
As for the rest, it's indeed hard to see anyone bettering/matching Kimi at that time. Montoya was occasionally very fast, but ultimately more inconsistent, which was proven to be the case in McLaren. Button I find an interesting case though. In BAR/Honda he seemed genuinely good, maybe he was a bit underrated due to his smooth style? How did he compare to Kimi in, say, 2004 or 2006, if later on you would consider Button in similar ballpark with Kimi? I think particularly in 2006 you could make a decent case of Button performing around Raikkonen's level, as Button had Barrichello well beaten that year.
Interesting to look at Massa at that time though. For three seasons he was driving in Sauber, twice got beaten by team-mates and narrowly beat JV. I mean surely nobody saw in 2005 that this guy would go on to match Kimi. Looking at 2004-2005 seasons it looks unquestionable Kimi was performing at a higher level though. In 2004 Massa was still busy getting outperformed by Fisichella.
By 2007 tyre war had ended, and Bridgestone 'control tyres' were introduced to everyone, or however they were called. Suddenly Kimi didn't look 'special'. Yeah, he still looked like a good, fast and competitive driver, but you could have said the same about Massa at that time. An adaptable fired-up driver like Alonso has been able to go through a variety of regulations and always maintained his relentless pace. But for some reason Kimi didn't or couldn't go at full lengths to adapt to these 'control tyres', and basically ever since then he has been doing catch-up in F1. Always somebody ahead of him in making car and tyres work.
As for people saying that Michelins made him look great. If you gave the same Michelins to everyone today, would Kimi blitz the field? Somehow I doubt about it. I think by now time has done its job frankly.