I am not an expert in cars, just try to understand things. Anyway in 10w-30 30 means viscosity/thickness of oil at engine operating temperature. For every moving part specific viscosity lubricant is required. for example grease is required at high pressure joints. using oil will be useless there. similarly grease can't be used in place of brake oil/power steering fluid.
As a general rule thick oil=higher engine drag so low performance & economy, low friction so longer engine life
thin oil= low resistance in moving parts, flows fast so better performance,economy and speed. but due to thinner film when parts slide they can get scratched.
In cuore's engine there are lot of sliding parts particularly value rockers that operate at very high pressure. In newer engines there are no such parts. so thinner oils in cuore, even if they give good performance are bad for longer life. Another problem with newer oils is lower anti friction agents as modern engines dont need them. they dont have parts sliding at high pressure as such parts are replaces by bearings. SM and SN have reduced anti friction agents.
A lot of people use newer oils in old engines claiming that they have new anti friction agents. might be true. other thing can be to use anti friction additives with these thin oils.
Cuore asks for 10W-30 with older grade. old grade means more additives. in new grade oils like SM and SN anti friction agents have been reduced and no problems as newer engines dont need these. but problem is for old engines.
now 20w-50 r thick for cuore but they have enough anti friction agents and detergents.