Can you provide a source for that theory having been debunked? I agree that data has been found that is at odds with the various neurochemical theories but am not aware of the neurochemistry link as a whole having been definitely debunked.
By all means, Google whatever you like, but if you show up to a doctors office waving WebMD sheets in a medical professionals face, you are going to be mocked and you deserve it.
So should I not have done my own research?
With that said, the first few search results for the query were from the journal Nature, the NIH, and Harvard university. Hardly the loony or malicious caricature that you attempt to paint.
The average medical professional is worst-placed to judge the veracity of any studies they find than the average engineer or mathematician who's done a solid statistics and probability course. Medical students are assessed on their ability to memorise and regurgitate facts, not on their ability to conduct statistical analysis.
The caveat you cite applies to basically any and all internet (or even media) consumption, and is therefore a non-argument.
I will say if you search for "chemical imbalance debunked" as discussed, the first result for me is a paper that also says dyslexia cannot be proved to be a disorder. Which just from vibes feels really conspiratorial, even without making comments on the veracity of the academic paper.