Rio - for me - had a significant drop followed by a resurgence: when he managed to adjust his game to his physical state (his back problems, not least, but also a general decline in terms of speed and so forth), his level went up again: he obviously didn't get back to prime standards, but still. He went from looking pretty much finished (that was the worst case scenario, you could say) - to looking pretty damn good for a player his age.
Blanc, by contrast, dropped down to a level he more or less stayed on (until he retired) - and that level wasn't very good, at least not consistently (he had the odd game where some of his old greatness would shine through, but on the whole he was a shadow of his former self).