Hard to imagine that a HD Service Manager would suggest "conventional oil" meaning "dinosaur drippings" after the 1k service on the newest engine. The Harley Syn3 and range of aftermarket synthetic oils out there are clearly better performing on the road and are proven in the lab. To top it off, Harley makes good bank on the Syn3

Maybe they meant conventional as in the same oil in all three holes? The worst synthetic suggested here is far better than conventional oils. I'd ask them to clarify, giving them the benefit of doubt. I'd never run dino-drippings ever again.