These are all good points, and I totally agree that when the infantry unit has 3-5 blocks, and especially if it has a leader, then just forcing it into square, and ideally keeping it there, is already a result. But, unlike Ney at Waterloo, cavalry should normally be held for the coup de grace ... not always possible I know. But when they can be, and you're looking for those last one or two banners for victory, the infantry are by then often reduced to, say, 2 blocks. Fodder for the cavalry, especially if you can find one without a leader.
Now I would say that even a 2-300 strong reduced battalion of infantry would be able to hold out against cavalry squadrons provided the square was formed in the first place. But in a recent game I deliberately targetted those weaker infantry units - the final victory banners came from reducing a two-block infantry to zero in two turns, and then using breakthrough to eliminate a one-block infantry unit in the rear of it. Neither had a leader, and my opponent had rather fortunately run out of cards for that section!
Don't forget, a 2 block unit is not just its numerical strength, but also represents its morale as well. Meaning in most cases that a 2 block unit is reaching its max level of punishment whether inflicted or even just its willingness to continue.
However, that said, I think the square rules in CCN 'Basic' (as we might now call it) is about right. Although a cavalry unit may well cause a casualty on a square 50% of time, or 67% if it has no leader, or if it is not an 'ignore flag' type unit. It is also 0% if uphill-downhill and other type an advantage against cavalry.
It also means that it ties up a cavalry unit for sometime indeed if the CAV unit's intent is to eliminate the square rather than freeze it in place to be blasted and/or to remove a card from the opponents hand.
But at this stage, albeit not having used the tacticians cards yet (I will wait for publication), I don't think the CAV need another 'assist' in breaking a square via a tactician card. To me, the balance is about right.