I've spent several hours of meetings with my boss, colleagues and an external consultant to discuss a certain topic. The external consultant has introduced the same topic in other departments of my company, but unfortunately he doesn't know what he is talking about. I once pointed out that the main example he is using for explaining it, was actually used as anti-example in the book, which we are using as reference. The book was written by the most popular evangelist and you won't find any book contradicting this aspect.
To make it worse two other colleagues are claiming to have worked on this topic in their previous department, whereas their explanation fulfills the whole anti-pattern checklist.
I'm explicitly not telling the topic to avoid distractions. I researched on my own and all the sources I found are stating the same about this aspect. I also discussed with experts on this topic in our company and they agree with me. I suggested to bring in those experts, but my boss rather wants to listen to somebody with "operational experience" (aka argument of authority), although our own experts have more real life experience from what I can tell.
To be clear, this is not a matter of taste or an implementation detail. It's about the fundamental definition. Let's say we're discussing cars and the consultant is explaining how you can drive from A to B, and that cars have 2 wheels. If you do not know cars, you won't recognize any problem, but if you inform yourself, you'll know that cars must have 4 wheels (ok ok, a few rare models have more or less than 4 wheels).
Now again I pointed out another fundamental mistake during a meeting. This was a mistake I explicitly mentioned to everyone beforehand and asked them to read at least the online summary on the topic, where it is listed explicitly as a common mistake (as it is in the book). During the meeting I again shared the link and the text, which is explaining the mistake. Nevertheless everybody except me voted to use the suggested approach. As this felt completely surreal to me, I didn't let go so easily and pressed to overhaul the decision - without success. Please note that I'm often characterized as less emotional, so I have good self-control and didn't get rude or anything.
Now I have the feeling that they are starting to see me as a grumbler, because I don't join their cargo cult. I don't think repeating the same thing over and over again will change anything. Still I don't want to contribute to this topic, because it's obviously wrong and I will waste more of my time without benefit.
By implementing this incorrectly we will not get any advantage but also no disadvantage, but it's affecting my motivation. By implementing it correctly our productivity would increase and increasing the productivity was stated as the main reason to work on this topic.
How can I convince my boss and team that the consultant and team colleagues are wrong, without looking stubborn or pedantic?
Addendum: Somehow many comments and answers are jumping to the conclusion that I'm trying to "counter-argument from my own authority". You may add this to your answer to address more scenarios, but it doesn't apply to my case. While pointing out the mistake, I explained the consequences and added the references to the book and other experts solely to emphasize that I didn't make this up on my own.