The Steve is Paul Tibbit Theory is a theory stating that went Steve from Blue's Clues went to college, he went missing but resurfaced years later as Paul Tibbitt.
Paul Tibbit's hair kind of resembles Steve's hair, except with lighter coloration.
SpongeBob being a relateable protagonist may have lead to Steve being replaced by Joe since Steve is too cool to be relateable by the average joe (rimshot), so Steve would have motivation to try and ruin SpongeBob.
It is possible that Paul Tibbit isn't actually his real name since no one would use their real name when ruining a beloved kids show.
Steve is too cool to be the same person as Paul Tibbit.
However, he could have turned to the dark side under the influence of biased Nick executives who only want money and not actual good products.