let me break this down
in ST, st old characters are hardly similar to ssf2 characters. that is a major misconception with people. st old characters are NOT like ssf2 characters. a basic example (not talking ae here only arcade st and ssf2) is fei long, in ssf2, only normals he can buffer are close s.fierce, jabs, shorts, and up close strong i believe. in ST, when you pick old fei, almost every normal he has, buffers. c.forward, c.strong, s.fierce far, etc. pretty large difference between st old and ssf2 characters.
so back to AE. when you pick super mode, you are getting the legitimate ssf2 version of that character. when you hold mode or start (depending on if you use xbox or ps2) when selecting super, you will get the ST old characters, hence the different icon during the fight.
this is a big confusion that most people have.
when you legitimately pick old sagat, hes been fucking nerfed to death. hes so slow. in ae, for the most part, they made old sagat basically the same as ssf2 sagat from what it feels like. if you want a sagat thats effective as hell, you have to pick hf sagat or ce sagat. and that shit aint gonna cut it if someone wants to use AE as an st only version, since hf/ce sagat will carry over the retarded dizzy properties.
hope this clears up a lot of confusion