I would agree that TSC was the most iconic level, and a fun one at that, but I don't know how Kotaku made the iconic=best connection. I think tropical environments get an unfair positive bias in games simply from the "wow factor".
Like you said though, I agree that AotCR was a better level in terms of combat engagement and diversity. That's honestly where I had most of my Halo CE campaign fun, partly due to the sheer size of the level.
To be fair, the author justified the vertical slice angle very well. TSC may be a better highlight reel, but AotCR is more intricate and subtle. Of course, it's also the most bombastic level: Banshees and Scorpions ahoy.
To TSC's credit, it's the ultimate Halo sandbox: you can dick around the island for hours, but AotCR is much more linear, even the exteriors.
I definitely hear ya. I felt that nearly every Halo CE level had a lot of the points the author was talking about, but often get overlooked due to their comparatively lackluster environments. It's easier to forgive stale gameplay with pretty trees and coastlines, much harder to in other environments. Not that I think TSC has stale gameplay, but in the same vein I think that its greatness is a tad exaggerated.