"Chemistry" as you're using the term here is a name for a set of models made by humans, not something in actual atoms and molecules. The atoms and molecules don't know that they're supposed to be doing "chemistry" instead of "quantum stuff".

When I say chemistry is fundamentally dependent on quantum effects, I mean the things atoms and molecules actually do would be impossible without quantum effects. The very existence of atoms depends on quantum effects; in a purely classical world atoms would be impossible. The chemical properties of atoms--their valences, for example--require quantum mechanics to explain.

Often in human models of chemistry, the details of how things like valences of atoms are produced from quantum effects are left out. But that doesn't mean quantum effects aren't being seen when we observe atoms with particular valences, for example. It just means the details aren't explicitly present in those models.

Depends on what exactly you do in chemistry. Understanding structures like molecules and chemical bonds takes you deep. I f you only care about macro effects, like how to turn this input into that output in an industrial process than you move away from the low-level basics.

The same as in any field, you get to choose if you want to invent new algorithms or if you care about software architecture - both valid jobs for a CS person but it's different worlds.

[0] https://www.edx.org/course/introduction-solid-state-chemistr...