My point is that rod bearings in Ninja 250s fail because of things like the oil level getting very low, or the bike being left outside in the rain with the oil filler cap off (actually read that here), not because the oil was not synthetic. Heck, I've run my '72 H2 on dino oil since 1978 when I got it, and never had a seizure or internal failure of anything. With a 4 stroke, clean oil kept at the correct level and changed at the recommended interval, and filters that are changed at the recommended interval are way more important than type of oil.
Use what you prefer, and don't worry so much.
