It was triple platinum in the first year it was out and then crept to 4x about 2.5 years after it was released. And Then There Was X was the massive seller, hitting 5x in a little over a year. Plus it had bigger singles.Even I agree with everything in this post, by your own logic and standard, It's Dark And Hell Is Hot is expected to be on this list considering it went 4X platinum. It's not there, so are you conceding that that IDAHIH isn't timeless?
That being said, his music has not stood the test of time when you consider how big he was and compare him to his contemporaries. Not to the extent of Bone, since he has more monthly listeners than Mobb Deep and bigger songs, but overall, I agree with the sentiment of what you are saying. Although, I think your usage of the word “timeless” is misplaced.