Humber may be ready, but he isn't ready to be a horse. Guerra was 2-6 with a 4.01 in the Florida State League, a pitcher friendly High A league so he is at the minimum 2 years away. Humber hasn't done well at all above AA...
Humber has had 1 year above AAA. It was the year after Tommy John surgury and he still led the league in WHIP, was 4th in K's (and only 19th in IP) and 10th in ERA which was well below the league average. He did pretty darn good in AAA if you ask me.