The engine builders I used for my MX bikes all believe you need higher cylinder pressures to force the rings out into the cylinder for good seal. Light but some load, fully warmed and use decel braking too. No high loads, like uphill 2 up WOT in too tall a gear, no steady RPMs for long lengths of time, don't leave it at 12k RPM for 10 miles. Watch a dyno run on a new engine and the more runs it makes to full RPM the higher the HP/tq goes as the rings seal better till it maxes out.
I believe the non syn oil at break in is due to the expense only and the need to change it early to wash out the engine of extra metals that scuff off early on.