Ok. I’m not sure what your point is. You’ve just made my excellently… even a basic fighter wielding a long sword does much more damage than cantrips at every level. You’re also not taking into account Magic resistance (common), energy resistance (relatively common) and immunity (common enough at level 11+)
Of course fighters have fighting styles, feats, Battlemaster powers, and the ubiquitous magic weapons etc. so they have plenty of their own resources.
The average die counts you’re referring to are for HP and in stat blocks when you don’t roll creature damage. Do you play that? You don’t roll creature damage? That’s not the way of working out averages certainly not for player attacks. If you’re going to be picky about it the. One 5, one 4, one 5 etc. alternating each die. The average is technically 13.5 but 14 will do.
It cracks me up that the people still think to argue this based on Fighter damage not being good enough. The maths has been proven time and time again on the threads. Do a search if you don’t believe me.