It's always so sad seeing these threads, not just for Pokemon, but similarly for when the Sonic Colors remake came out on Switch and the busted Ocarina of Time on the Switch's N64 service. Methods to send feedback/complaints actually exist, and enough people getting involved in it can make a difference, but everytime people on here will try and stop you doing it, and discourage other people from doing it. You love to complain, but you don't want to do anything about it that might result in change, and even more you hate the idea of other people being proactive.
In short: send a complaint to the links in the OP, and also contact Nintendo's customer service. The customer service will pass on messages to the developers if they seem legitimate, and even better if they are receiving many messages in relatively quick succession. Don't act like a dickhead in the complaint you're sending, talk like a reasonable person. Explain the situation, the trailers for the game used music that was not indicative of the music actually used in the game, meaning the advertisements were intentionally misleading. Your expectation was that the game would include higher quality music than was included in the original DS Diamond and Pearl and the trailers indicated that the game included an updated soundtrack, but in the released game there is only the original music ported directed from the original DS game and with low-quality midi instruments so the audio actually sounds worse.