Except Kei doesn't have a disease. Kei is a 5"9" man struggling to compete with a Tour where the average player is over 6ft tall.
At least Chang, in his day competed with people under 6ft (Agassi, McEnroe) but Chang, especially toward the end of career, struggled physically to keep up with a Tour that was being increasingly filled with taller and taller player. Kei has rarely had that luxury. Much like Rubin, their bodies, while appearing fragile, are actually being gradually worn down from having to compete against much bigger, stronger players.
I actually think Venus has competed a lot more often (ailments and all) than Kei on their respective Tours.
Meanwhile,
The 20-21 year olds are definitely having their say this weekend! Coric is playing really aggressive and I'm enjoying seeing it!