Charles Oakley says even though the dude's a LEGEND in New York, Patrick Ewing simply ain't the right guy to take over for David Fizdale as Knicks head coach.

But, don't worry, Oak's got someone in mind -- Mark Jackson!!

TMZ Sports spoke with the ex-NY star about the coaching vacancy ... and, while he lists off a number of ex-Knicks who are qualified for the gig, Ewing ain't one of them.

Why??