I actually have to agree with this. In Sonic Generations it was definitely done better. I'm not sure if it's to do with how they composed it or simply the choice in "instruments" but they do sound off. On the offhand some of the remixed tracks from older games sounded pretty alright like the vs. Metal Sonic theme.
one thing that bugs me though is the fact that the Spaceport theme sounded like a rip from Sonic Colors, if I'm not mistaken it sounds relatively close to Sweet Mountain Act 1 just with a bit of variation on some of the notes in different parts and of course the lyrics
in hopes of confirming that i'm not just speculating here's spaceport and here's sweet mountain and as a bonus the game land variant of sweet mountain
it's mostly similar in the first notes but i cant help but wonder if i'm just projecting