Back to maths class!
"Basically raw capacity is doubling every generation with compressed capacity increasing 2.5 times per generation."
No, that's not mathematically possible. Compressed capacity increases at the same rate as uncompressed, assuming no change in compression efficiency. And indeed compression has pretty much stopped evolving: all the low-hanging fruit has been plucked, there are only minimal gains left to be made.
What's worse, a lot of the new data which is filling up these tape drives is made up of images and video, already compressed: so the stated 2.5:1 compression ratio is actually falling.