it really is one of the best ones, i had never heard it until scawful/freakyfurball posted it sometime in 2013 and it pretty quickly became a favourite. it being the final champion battle theme on a Nintendo DS Pokémon game also makes it feel like a swansong for the console itself, they really figured out how to make the console produce bangers at the end of its lifecycle. not that prior games didn't have good soundtracks, but i remember feeling really impressed by the final battle theme from Bowser's Inside Story too.

all this being especially compounded by the fact that i found early Nintendo 3DS games to kinda have subpar soundtracks. i think this was mostly caused by the speakers on the 3DS just being kinda meh in general, i recall hearing once that some games shipped with an alternate version of the soundtrack for when you have headphones plugged in...

as for my current opinion on 3DS game soundtracks, these are my favourite wild pokemon and trainer battle themes right now: