In regard to the Breen, I would note that Star Trek Adventures: Klingon Core Rulebook says "They only
present themselves to non-Breen in full-body suits that hide
their identities, and their bodies disintegrate when they die
while wearing those suits. While this is an admirable trait – it
means Breen cannot be taken prisoner, an attitude in line
with the teachings of Kahless – it has made it impossible to
determine the true face of the Breen." This is a pretty cool explanation for how Worf could be right even after Kira and Dukat stole their suits.
I know STA isn't canon but I still like this reasoning.
I like the idea that the Breen bodies loose consistency upon death, especially if they're more gelatinous in their natural form, as these episodes of DIS appear to be presenting them.
However, I do not envy Kira and Dukat having to scoop a bunch of Breen jello out those helmets before putting them on.