Link: https://www.nature.com/articles/d41586-026-00594-w

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Sharks might not be a natural biological group, with most species potentially closer kin to rays than to an oddball group of sharks.

The results, which haven’t been peer reviewed, suggest that most animals that people call sharks are more closely related to rays and skates than to hexanchiform shark species — just as Gould pointed was the case for some species called fishes. Biologists call such groups paraphyletic.

I mean yeah...

They're like crabs, "shark" is the final form for large marine predators.

But just in general, I thought this was the case with fish too? Like isn't there just so many weird "fish" that taxonomically almost anything can be a fish?

Just because evolution ends up in the same place. Doesn't mean it always took the same road.

It's seems like what we really need is a system to identify lineage and a system of grouping for current form.

There does appear to be a formal definition as well as an informal one:

Sharks are a group of elasmobranch cartilaginous fishes characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii[1] and are the sister group to the Batomorphi (rays and skates). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts.