Now, as far as Rohan goes, there are several problems with the Rohirim as they are right now. There are inherant issues with Cavalry making them less effective than they could be, but some of those shortcomings can be overcome through strategy and situation. However, regarding the Rohan army specifically:
I agree that they should have a way to legally field an all horse army, either by paying less for those without bows, or by giving them an option to circumvent the bow limit on their horses. Other units, such as the Dunedain, have those kind of options. Since this is a skirmish game and most of the skirmishes were all horse forces, this only makes sense.
I agree that Gondor should have heavier armour and lances. The Swan Knights should be particularly well armoured but more rare. I would love to see Rohan with lances, because of how their long spears are used in the books, but I understand that this is more about what we see in the movies.