You find it interesting that people that play the exact same role on both teams can be rivals?
By your logic golfers could never be rivals, because they're never interacting or defending against one another -- they're just playing against the course.
> there are people on both teams who really are tackling those guys.
This is the critical distinction.
Why is the commentator talking about Brady vs Peyton, when actually Peyton is doing nothing to stop Brady getting touchdowns?
Why don't they focus on whoever is making the decisions on the defensive side? That would seem to matter more as a struggle between combatants. It's not like each defense is some nameless, generic unit that simply reveals who is the better QB.
There might be some depth to the attack vs defense strategy that is worth highlighting, above the QB v QB.