That's all they've changed?

Ariel probably is the worst character as far as female protagonists go, but in my opinion she is the most beautiful Disney princess.

You forget that the mermaid's reason for leaving the sea was to marry a human and gain a soul. She could not do that in the sea.

You forgot TLM putting on a suit of armour and matrix ninja'ing an army of incompetent males to death like it was nothing.

From today’s perspective, Ariel is definitely an outdated character.

Nevertheless, compared to the earlier Disney princesses, she is much more modern and was a first step in the right direction.
The fact that she is willing to give up her friends and family for a man she doesn’t know at all is pretty stupid from today’s perspective and anything but romantic.
Also that she sells her soul to get a body that she thinks a man will like.
A song like “Kiss the Girl” also seems outdated nowadays.

But Ariel also has positive qualities:

Although her father doesn’t allow her to, she is interested in education and wants to learn.

Unlike her completely passive predecessors like Snow White, Aurora or Cinderella, she takes her fate into her own hands. She actively goes to Ursula to do something for her own happiness, instead of waiting for “her prince to come someday.”

Although Ursula is eventually defeated by Eric, Ariel is not completely passive and at one point tries to defeat Ursula so that she will not shoot Eric.

Ariel is rebellious, which is revealed not only in her behavior, but also in her “clothing”; the colors of her sisters’ bras match the color of their respective tails, but Ariel’s do not.

I also think it's positive that Ariel doesn't want to live on land solely because of Eric. Long before she saw him, she wanted to live there and collected all kinds of doodads. So she's not exclusively interested in a man, or in other words, her only interest is not in marrying a man.

Compared to the earlier princesses, you notice with Ariel that Disney has gone in a new, modern direction here.