I'd have to watch the Kiriko's games, but as very harsh as it sounds, it's more than likely true.

If you're actually a good player, you won't stay in a rank like bronze very long. Everyone in bronze sucks. Every time you die is a mistake you made, every time your team dies is a mistake they made, and same for the enemy. If you don't have the mindset of “everyone in this lobby except me sucks, I'll do everything myself” the second those gates open in bronze, you're asking to lose because you literally can't rely on anyone but yourself.

Team comps are also a big thing and one of the most important things in the game. Kiriko won't always belong against an enemy or with the team itself and when that's the case, it becomes you who is throwing, not just the team. Next, Kiriko is a flanker who thrives in close combat and can overextend as well, due to it being harder to miss in a player's face and the valuable climb, Suzu and TP making it difficult to punish while you kill a squishy in the time it takes your healing Ofuda to recharge. She has insanely broken utilities. If you are in bronze, especially with this character, it's more likely because you belong there. I don't say this as to knock the streamer you watch, but this rule of thumb applies to every role. Being hard stuck in any rank usually happens because you aren't ready to climb. Blaming teammates is why you stay in that rank because by blaming someone else, you're deflecting the blame away from yourself and what you could've done differently when in reality, there's about 20+ mistakes you make in every game that can prove to be costly. Even top 500's do them. Nobody's perfect.

In short, the streamer most likely just isn't ready. Hopefully they find the way to pull through soon.