I was there when Perfect Legend made this statement and while I didn't dwell on it then, I've thought about it some and I find myself agreeing with the statement.
I mean, I won't dare say that he is a terrible character. With a six-frame anti-air (and an X-ray that works similarly), great damage for his combos, and a divekick that can cover space and recover instantly on whiff, he's far from shit-tier. But given that the first hit of each of his usual blockstrings can be ducked and counter-poked, and with how limited his mix-ups have become, it isn't as easy for him to be a rushdown character like it used to be. The spin is a great way to escape pressure, but is so unsafe that it can be baited and punished.
His zoning isn't that impressive, either. Low Hat is easily jumped and even his regular Hat Toss with shifting directions makes little difference. He will accomplish nothing if he's not up in their face.
Teleport is decent, even his EX version, but they're too easily beaten unless your character lacks armor and/or great pokes.
I tried to replace my Raiden with Kung Lao in an effort to cover Sonya's bad match-ups better, as
Tom Brady once advised me to do down in Plano, but I simply could not be successful with the character and eventually I dropped him in favor of the Thunder God. He just isn't who he used to be. This is not to say he can't be viable, but it's an uphill battle for him to reach that level.