If you are just doing a simple analysis on combat performance then your friend is correct.
However, when you take into account that cavalry have many other attributes not shared by close order infantry I am not sure you can claim that they are underpointed.
1 They are not march blocked by nearby enemy units.
2 They move much more quickly and therefore will nearly always charge infantry generating momentum tokens
3 They can counter charge and therefore get charge benefits
4 They can disengage infantry with impunity
5 They have the speed and maneuverability to more easily get around flanks and to prevent this will often require a couple of infantry units to be positioned to stop this.
6 A cavalry unit in the flank/rear is not a pleasant experience for formed infantry even if they pass their cohesion test.
This is not a complete list - personally I think they are under pointed, but then I am terrible at using cavalry!