I’m not able to give a full answer, but the factor that strikes me is the income that’s been taken over the years. Are you sure you’re taking this into consideration?
I have investments that give very modest capital growth but a decent income which I don’t re- invest, if I re- invested it the capital growth would be far higher.
You can’t have your cake and eat it, if income has been taken over the full period that may explain the limited capital growth.