So, if it is a problem that people tend to make huge blobs of units and crash them at the enemy, something should be done about it. Everything in the game seems to scale so that it is always better to split a huge blob into smaller ones - like it is more efficient to have many estates than a single large one, or many different units instead of one huge. But the question then is essentially how to change this so that the same is true on an army level.
Sure, there are methods already there, like crowded roads. But that is a hindrance, not an encouragement. Would we perhaps benefit from such encouragements, like giving more power to raiding parties somehow? What if it somehow hurt more to have enemy troops present on a number of regions? If you only march your troops in one or two enemy regions, no problem, the population can take that. But what if there were increased morale penalties throughout the realm if many regions were simultaneously under attack? All you need then is a small force to cross the border and spread around the place, so you only need a little bit stronger force to counter it, but then.. and so it becomes a game of guessing what the other will do.
This proposal probably has its problems and it may not be a perfect one, but perhaps we could think of more ways how it would actually be beneficial to split the forces most of the time. When conquering a city, you might still want to blob it and that would perhaps be fine, but for the rest of the time it could be different.
It's a lot because of player culture. As general, on BT, I've often divided our forces to great success.
All depends on what you want to do, though, where you are fighting and how strong the enemy is. Blobs are necessary when you must defeat a blob army, however, or take on fortified positions.
In a battle superior numbers/training/skill will generally prevail, though it is no certainty. In a war numbers are a smaller part of the big picture. It shouldn't be a case that you need similar CS to be competitive, strategy should play a much bigger part then it currently does.
Larger force + better/equal leadership should generally lead to a win. Right now the larger force doesn't need to be particularly well led, just not totally incompetent.
You confuse army size with army strength. If an army has a lot of CS, it doesn't mean that it is large (though it usually is), but rather that it is very strong. A small army with more CS than a large army should, theoretically, win over the larger one.
