Genshin impact

Thanks for the tip about the Pyro Cube; I'll try equipping Mona with damage stats next time.

I don't think it's even necessary to equip a Hydro character with damage stats. The shield is removed simply by triggering a reaction, and "Vaporize" works best. I saw a streamer defeat a level 50 Barbarian – I doubt she was equipped for damage.

I definitely can't defeat the Samurai in 50 seconds.

Actually, I didn't manage it on my second try either. It took me almost a minute and a half, but that still left me with enough time to deal with the Fatui.
I used the same team composition as before – the one listed in my profile. In the first half, they all buff each other's energy and spam their ultimates on cooldown. I'm actually glad I got Ayaka; without her, I would probably have used Hu Tao in the first half. I think it would have been difficult for Kazuha to quickly defeat the last, tough Samurai on his own, as he likes to heal. But in general, people say that teams focused on Freeze work well against them.

Who should I take... Raiden or Ganyu?

If I had to choose between the two, I would also choose Ganyu. But... Yae Miko.
By the way, it seems that Raiden and Kokomi will be released in the next patch (2.1), although the order is unknown. And Kazuha's rerun will be in 2.2. Of course, if the leaks are to be believed.

Added 8 minutes later
I posted it on the database.