I agree with you on your point.

I'd like to stree that the inheritance contributes the power of the object oriented programming.
Therefore, all the method must be overridable. We do not have to say it. If we cannot override method freely, what's the purpose of using the OO language.
That's why, the keyword overridable and overrides are redundant to me and the fact that we cannot override methods without them defeats the purpose of the OO programming in my
mind.

Only when we don't want a programmers to inherit methods, then putting 'Final' keyword to stop make sense. VB.NET makes all the methods 'Final' without overridable and overrides. Just as mention, VB.NET makes us talk too much!