It doesn't matter how many sub-class a class has, the only thing which matter is how many methods could be called from a given line of code. e.g. a method could have two implementations across four class, but if only one is called, it will be as if the methods had only one implementation.
The get an idea of the cost based on the number of implementations which can be called. Performance of inlined virtual method invocations in Java
Profile driven inlining is likely to be inlining based on methods actually called.