for the downside - countless cultures have had preventative mechanism for that.

if your biological child is an idiot/wasteman - then you could adopt - the Roman Empire ran on adopted children, with biological children seen as wasteman.

the other way it's done e.g with Japanese businesses - again adopt your son in law and give him your surname.

the thing about giving helm to the sons - is usually you would've had a whole lifetime to evaluate the candidate 20+ years. do mistakes happen yeah, but honestly the risk is overblown.