Bilingualism has a major disadvantage:
The cited study postulates in the discussion that Tip of Tongue events come from simple reduced frequency of use in any given word stemming from a much larger lexicon. There's no evidence at all suggest that there's actually a neurological disadvantage to bilingualism.
Also, it seems pretty counterintuitive to think that practice in an entirely new cognitive arena, something like a new language, could do anything but improve your ability to process language. If there's a paper out there I'd love to read it.
Knowing multiple languages is extremely valuable.
That hardly makes it the only one that matters. I personally have derived enormous benefits from studying Latin. There have been several times I have wished I spoke Spanish and a few times I had wished I could speak Japanese, Pashtun, Arabic, and Dari.
Knowing more languages is definitely a good thing.