Suppose half of the sectors of the economy grow forever at 4%, while the rest completely stagnate.  I’m strongly tempted to say that this economy’s growth rate equals 2% forever.  Anyone tempted to disagree?  If so, why?

Before you answer: Would it matter if the 4%-growth sectors were all in “virtual reality” – and the stagnant sectors were for actual food, shelter, cars, etc.?  If it matters, why does it matter?