6 years of evil medical school doesn't qualify as professional credentials? Also I'd put Dr. Phil below most of these guys, although maybe slightly above Hannibal Lector still.
Dr. Dre and Dr. Venture: Both possess honorary doctorates. The former from UCLA, the latter from a Tijuana community college.
Dr. Pepper: Charles T. Pepper did have a medical doctorate. He is cited as a possible source of the name.
Dr. Evil: Evil medical school.
Zoidberg: Claims he lost it in a volcano, more likely a art history degree.
Dr. Horrible: Likely physics though he claims Horribleness (though it could be a catchphrase.)
Dr. Seuss: Intended to get a Doctorate of Philosophy, got an honorary doctorate of Humane Letters.
The Doctor: Per This - While pretending to be the Doctor in an effort to save herself from an army of Cybermen, one of the planet’s deadliest enemies, in Death in Heaven, Clara said: ‘I don’t even really have a doctorate. Well Glasgow University, but then I accidentally graduated in the wrong century.’
Doc: Does become a doctor at Storybrooke hospital in a live action show, "Once Upon a Time", apparently not a surgeon though.
Spin Doctors: No doctors.
I feel like a fair amount of those on the trained side aren't medical doctors (Phil, Ock, Robotnik, Lector, Honeydew) or at the very least, aren't folks you'd want around for your heart attack.
There is no way Dr. Mario has any training. He just throws random pills at the problems hoping that they line up and do something other than cause an overdose.
Why is Doctor Strange to the left of JD from Scrubs? Isn't he a world renown surgeon or something? Does that count for less because he hasn't had medical practice lately?
Dr. Zoidberg is a fully-qualified medical doctor, though, and a good one at that. Just not for humans. Even so, he's quite good, given that he hasn't killed any of his human patients, though they may come out a little different.
As is Doctor Who, who has high qualifications in literally everything. It took them a few goes, but they got there in the end.