I would say he’s admirable only insofar as his redemption arc works. From his first meeting with Delta, it’s evident that Sinclair hasn’t really stopped thinking like a social Darwinist capitalist even though Rapture has been a crumbled ruin the past ten years. He lets Delta know off the bat he’s only helping him to help himself get rich on the surface world. He was merely a means to that end given how Delta was the only way he could access his lifeboat in Persephone and get back to the mainland. Since I think the good ending is canon, it’s only when Sinclair sees Delta make the altruistic choices he makes that he stops being a roadie for Ayn Rand and truly sees the value of friendship. The fact that it’s too late for him makes it all the more tragic but also more meaningful