I don't find you to be douchey at all, I like to discuss grammar!
So first, one does not have to conjoin two independent clauses. And while one can understand what is said in your first sentence, I am positive it is not grammatically correct. Here's why:
1) You do not have two independent clauses in your first sentence. "I'm fairly convinced that your reading is" is actually a dependent clause. Since you do not clarify what the 'is' actually.. is, the meaning of the sentence is entirely dependent on what the clause before it justifies. I'm fairly certain that explaining the misunderstanding in your first sentence would be enough to exemplify the struggle throughout our grammatical debate; however, if you are not satisfied you are welcome to read on as I address your further points.
2) "Only" as a conjunction is standard English usage; however, still informal / can be construed as slang. This conception is what I addressed in my first post--in order for maximum clarity of the statement it would have been much better had the author written their intention instead of leaving it to the imaginative boundaries of vagueness.
3) If you go back to my original comment on the second comma, I actually noted, was problematic in terms of grammatical structure. So I agree, it is both common and erroneous. And if I did not note that clearly enough, I apologize.
Furthermore, the examples from the OED are all fundamentally different than the Kelsey Moser sentence which started this all. All three of the examples listed offer a clear subject to which the pronoun after the 'only' is affixed.
Shakespeare: ... all I... only give me...;
Spurgeon: Many a man... only he...;
i-D: ....but she wants Eddy, only he....
In all three examples the pronoun used beforehand is clearly defined, leaving the follow-up clauses as dependent on the definition introduced in the first independent clause. In the example of:
WE in China is like Team SoloMid in North America, only people who don’t play League of Legends are WE fans.
I stick by my point that both sentences are independent clauses, and as such can not be conjoined by an 'only.'