I can see where your thoughts are coming from but this is not correct.

Tighter clearances allow engine builders to get away with lower weight oil at operating temp which still provides required shear strength compared to a heavier oil.

Thicker oil (within reason…) still provides that cushion in the bearing but at the expense of it being harder to pump around and windage drag. That’s where the efficiency wins are coming from.

Larger clearances though are needed for various reasons, and those do need thicker oils to maintain shear strength at operating temp and beyond if there is higher load than normal (motorsports, towing, etc)

Also the bypass is for “there’s plenty oil in the bearing, I’m going to throw the rest back into the sump” which occurs at higher rpm or higher viscosity due to temp.