When you ask an individual at a dealership, you get HIS opinion. Working for a dealer gets him not one step closer to facts, figures, and truths. So, he quits a Honda and Suzuki shop, goes to work for Yamaha, and now suddenly is a Yamaha expert?
Use some logic. If an oil was so slippery it prevented break in, we'd all run it. Your engine would never wear again. That would be awesome, and it would change the world. No moving equipment would wear..ever. No way, no how.
Back in 1986, your mechanic heard synthetic oils were "too slippery". That sounded reasonable, and he's been repeating it, ever since.
Oh, nevermind..I know better than to post in an oil thread, and did it anyway...Urinate in the gearbox if you want to....