I think he accomplished a great deal in regards to bringing attention (and high level recruits) to HBCU's. For him to bail for more exposure and more money seems a bit hypocritical but let's be honest - none of that crap matters in major sports. If he wins there all will be good.
He didn't bring any additional attention to HBCUs, at least nothing at all tangible. He did a little tiny bit for bringing a bit more exposure to the SWAC, but if you ask people today talking about Deion what conference Jackson State is in, most couldn't tell you if you spotted them the S and the W. He did bring exposure to Jackson State but it's going to leave with him and not have any kind of a legacy.
To be clear, I'm fine with him not doing anything for any other entity other than Jackson State football and Prime Inc. but I don't, at all, love many white people giving him credit for doing anything other than helping himself. Like rusty said, he's no different than most FBS college football coaches, he's no HCBU savior.