the games have a really slow pace and mid gameplay

This was my main gripe with Sunless Sea and one of the reasons I vastly prefer Skies: far less back-and-forth / grinding. It moves along a lot more, even if still slow-paced at times.

Also and to add to your list: A House of Many Doors - extremely close to both Sea and Skies. It's good.

Is Outer Wilds indie ?

Eleven people team, first mainstream game, studio unknown before it; I say yes.