If there is a magic cheap structure to stop all cavalry perfectly then why would anyone concerned about Strat ever spec into cavalry? Or buy horses? Cavalry is by far the most expensive type of troop to equip on Strategus, and I think it's silly to suggest that they should just be negated by cheap items like ladders. Finally, about your last two sentences; just because something hasn't been caught as being wrong in the past doesn't mean it can't be caught as being wrong in the present.
Agreed on cheap and easy, but as Zapper mentioned there are ways around that too. Securing your own forward spawn, having a good arcehry and perhaps even catapult position to target tight formations, by that then provoking the defender into changing positions.
I would like to see that you would be able to built spike defenses out of construction materials, like 1 c-site + 5 materials, those perhaps maximum length of a small ladder, but huge amount of hitpoints . They are fairly easy to spot and when you would build a couple of those would be able to protect an area effectivly. As they are easy to spot, catapults could then be used effectivly against them in opposite to ladders on the ground. With such spike walls but as with siege shields there should be a maximum you would be able to build.
It is not about blaming who uses laddering atm, as most of us did or still will do as long there is no ruling.
Everything what you use aslong it is not game breaking it can be done further. Now that but depends on point of view here, aslong you don't put ladders directly on the flags, they really are just a fortification and cavalary will notice where they are and if those cav players communicate they can just easily avoid those ladders till at some point one site got close enough to destroy those ladders. Till then cav cant easily spawn kill or easily lance certain positions, those positions need to be conquered or handled by ranged and infantry and there is by default nothing wrong with that.
Also who says attackers should have higher k/d anyways, they are the invaders, the aggressors, the once who are in uncertain foreign territory. The advantage of attackers will always be, they came to a time often not expected by the defenders, by that often they have better or more balanced equipment. The defender should have the terrain bonus(which often through random maps doesn't work out too).