You're adding an extra noun! It's not "someone who verbs nouns", it's just "someone who verbs". Example: A birder is not "someone who birds birds", it's just "someone who birds", with "bird" meaning "to observe birds". This is easier to see with simpler nouns. Welder = someone who welds. Racer = someone who races. Yodeler = someone who yodels. Singer = someone who sings. The meaning is inconsistent because the verb is different every time! You're not being given a noun and have to guess the verb. You're being given the verb directly. If you don't know what that verb means then yeah you have to look it up, just like EVERY OTHER WORD IN EXISTENCE.

Edit:

I really, really don’t know how to break this down simpler for you, okay?

You can keep saying stuff like this but every time you do I only relish the irony.

Anyways I decided an example that can't even have a noun might be helpful. This works with any intransitive verb, but the best example I have is probably "worker" = "someone who works". You could also use "yawner", "laugher", "walker", "carer", etc.