It's neither impossible nor impractical.
In a bit of abstraction on the general military situation of the game, on default, a kingdom, at the start of the game, on average, has around 6~7 towns + around 9~12 castles + 9-10 clans. At the very start the troop numbers are low and is not at the full potential of what those territories and clans may achieve, but in a few years all kingdoms arrive at around:
* Total force 6,000~7,000-ish
* Around 30% of total force tied up as garrison = 1,800 - 2,000-ish
* Around 70% of total force as fielded troops = 4,000 - 5,000-ish
* Field troops led by 40-50 lords from those 10 clans = average size of parties 100~120-ish
In a typical war, not all parties in the kingdom show up at the same time. Usually the ones that may potentially gain land from the war, is the most likely to take part in the war, but about a quarter of the lords and their parties seem to never show up, and just do their own thing. Also, logistical differences such as relative distance, different army mustering locations and etc.. give out a staggered advance of enemy forces into your kingdom.
And thus, in an average war, of the 4,000 - 5,000 fielded troops an enemy kingdom has, the expected total invasion force is around 3,500 soldiers at the max. And due to reasons stated above they always come in staggered waves of armies consisting of anywhere between 800~1,500. It is very rare to see an AI enemy army that musters more than 1,500, and stuff like 1,700~2,000 are pretty rare.
So they usually come in at either 4 waves of 800-ish, or 3 waves 1,300-ish, consisting of around 30 parties.
Which means the following:
(1) You don't necessarily have to permanently keep anyone prisoner. At any given time, if you can maintain the current number of prisoners to over 25, ideally around 30, then effectively the enemy's fielded troop force is annihilated.
(2) Even if the lords escape in large enough number to form a new army, the overall size and quality of the army is severely diminished, with something like more than 1/3rd of their force being recruits or t1~2, making it super-easy to just crush them again and take them back as prisoner.
(3) With all of the above information, the best strategy in a war becomes to...
(a) wait for each of the 3~4 waves of enemy armies to wade into your territory
(b) when the incoming army initiates a siege, either gather a bigger a force right next to them, or get yourself involved in siege defense to destroy the army and hold all lords prisoner
(c) repeat the process about 3 times and effectively you've taken in most of the enemy lords that can fight at the moment.
(d) from this point on, is where you start a counter-offensive and hit out at enemy fiefs, because there is no enemy left to really challenge your own armies any more.
Usually, this strategy works well enough without even any of the escape chance related perks. Once around total 3,000 enemy soldiers are annihilated, from that point on you can leisurely lay siege, build 4x trebuchets to bring down the walls each time, and then repeat this about 3 times to take 3 enemy towns.... at which point the war will come to an end with them paying tribute.