https://en.wikipedia.org/wiki/The_Little_Mermaid
I highly doubt current identity politics were on the mind of the original writer when conceiving the story originally.
As for the Ursula stuff, if 'feminist' was the archetype they were going for, they certainly managed to portray feminists in a fairly negative and terrible way. Ursula was not a sympathetic character by any stretch of the imagination.
Nothing wrong if people want to interpret the story that way, that's the thing about good fiction, it makes you think and can tell a different message based on perception, but I doubt it was intentionally subversive and written with those ideas in mind.