I think Rio 2 is a better, more dynamic score and songs than Rio 1 overall (I listen to both soundtracks in film order), but you're right that the sequel's crappy plot - piss-poor pacing and ending - actively makes the score worse than the sum of its parts.

While I sometimes mentally flip-flop between Dragon 1 and Dragon 2 as being better, I generally think 2 comes out on top and is Powell's very best score. Not only does it plus on the original in most aspects, there's also not a single dull moment in that entire score; the first score's original 25-track album back in 2010 is an absolutely perfect curation, while the full presentation on the Deluxe Edition is still excellent but slightly less well-paced. Dragon 3 is at a respectable third place; I ponder if it's a weak ***** or a ****½, but there are some nitpicks holding it back from 1 and 2.