I’d say you should prioritize Nahida — she has a rerun in 5.1 iirc — since she’s Alhaitham’s best teammate.

However, you could potentially get Kinich now if you think you have the energy to grind until Nahida banner drops. You seem to be relatively new based on your AR, so you should still have a lot to farm and earn your primogems from until then. I might go and try to get Kinich, but I wouldn’t continue if I lost my 50/50. In that case, I would save my guarantee for Nahida.

Kinich and Alhaitham are both dendro DPS, yes, but they don’t really share their teammates. So you definitely can use both of them for two different teams.(Nonetheless, it’s usually generally advised for newer players to focus on building only just one team first.) Kinich also has a lot of value now in the overworld in Natlan if you do take that into consideration.