[kaba0]

You are comparing having a feature vs not having it. To make it fair you have to provide for polymorphism, and at that point most of your points become moot in lower level languages as well. Also, bounded subclassing exists (sealed/final classes) so in theory most/some of the optimizations you mention are possible.

[adgjlsfhk1]

IMO, the best way to do this is to provide multimethods to give you both polymorphism while letting the compiler know how objects are laid out.