There will always be differences in characterization

Even in the 90s. For example Yamaguchi portrayed Sonic as a cool loner, but other artwork from the period showed Sonic in a cutesy manner

I think the way Sonic is presented doesn't matter much, but more so his personality. While there certainly were creative differences, overall there was a consistent enough vision for Sonic as a character in Japan between 1991 and 2009. The problem is that Sonic as a character is kind of a vague ideal and so different writers will have him speak and act in different ways.

There was a clear effort beginning in 2010 to heavily alter who Sonic was or what he was about at his core, especially in the English script of the games