Unfortunately I don't have all the answers, but here is my analysis.

The chain is spaced for the pins at ½".

If a tooth on your cassette wears uniformly, then the spacing will remain at ½". A longer chain wouldn't necessarily dig deeper into the cassette (where spacing is shorter), but might ride a bit higher, and thus add a bit more angle to the bottom of the tooth, and narrow the top of the tooth.

As the chain wears, however, much of the pressure gets transferred to the last tooth on the cassette or chainring, with the chain essentially slack over the rest of the teeth.

The good thing about the cassette is that it rotates in relation to your crank stroke, so it will wear uniformly.

I did manage to prematurely wear out one of my chain rings by allowing the chain to stretch too much. It was the 42T chainring. The 54 is worn, but hasn't caused me a problem. With the 42, I would tend to stand while pedalling, so I had an uneven stroke. This meant I ended up with more wear during the power phase of the stroke than the top/bottom of the stroke. With the replacement chain, it made a lot of noise, but otherwise worked.

A couple of chains back also tarted breaking after too much wear, which was frustrating.

Anyway, go ahead and replace the chain, then see how the bike rides before replacing more parts. You'll notice either increased drivetrain noise, or skipping.