Yes, i see your point and you are right of course .
And I expect that adding caps is often the cause of fast deterioration of encoders.
That said, i expect an encoder to work out of the box as the Alps does formidably.
If you open quality encoders, you will find wipers that are separated into several contacts and sometimes even additionally staggered. All done so they don't bounce all at once, and the contact stays connected.
Cheapo encoders mostly don't have that. In fact, here is a picture of that bad example: single wiper contact as expected.

And of course, the secret sauce is in the contact material.