I've supported TsubaHono for like 6 months now, sarcasm not needed Nothing beats RinPana (the image got it right, the pure pair that knows each other so well)
A few things about the matching. The game does match you against people that are around your strength generally. The thing is, if you enter a winning streak, the game PURPOSEFULLY puts you into matches where you are to lose (AKA being matched against stronger players). That's where the bots come in, the game is trying to match you against stronger players, but if there aren't that many players playing at the time, they use bots to kick your ass instead
The game pretty much tries to keep your placement average around 2~3 area.
Now, the reaason people would use weakened teams is so they have a chance against players as opposed to bots. No matter what, the bots will just RNG off the first person in the lobby (unless that person fails, only condition that this changes) so it's all luck. When you're playing against other players, combo counts a bit for your score, so if you severely outcombo someone, you can beat them. Also, players occasionally dodge songsthey don't want to play, so you get free placement. I personally dodge every single match that's 2 or more bots.
A small random thing, if you are the 1st person in a room, 1 other player joins, then 2 bots, if you dodge, you're giving them a free with essentially because of the "host" dodges, so do the bots. I do this to help other players out ~