Objectively speaking the characters most endangered by this are those with strong defining traits, most notably Kai.
I wouldn't consider it flanderization though, because Shen leverages the Xenophobia well, uses it as comic relief, and it matches up with Kai's backstory.
I wouldn't say Seiun because he hasn't been in the story for long and hasn't done much. A good way to judge this is to test whether the character leaves very similar impressions on everyone.
Example Kin, who if we were all to describe her in a phrase or less, we'd almost all say something along the lines of Kin x sharp objects, or just stab happy.
Kin's main trait is simply she likes killing things. There doesn't seem to be much else going on in her head. She was leveraged for exactly that purpose though, and she's kinda just a side character.