Coping with the lack of dismouting.

Having just destroyed a couple of Venetian armies with my cavalry focused army, I realised I was unable to exploit my sucessive victories simply because ... they have Italian spear militia in their cities.

All my cavalry units, even Kataphracts, would simply be butchered in the streets , without the ability to charge, while my Byzantine Spearmen are simply incapabe of combating the far superior Italian foot units.

Therefore, I would like to ask how you people cope with this absurd lack of an ability to dismount, and to implore CA to please add in this feature, especially since it was present in MTW.

I agree it is ridiculous that the ability to dismount cavalry was left out but it's not that difficult to get around. Just don't use an army comprised entirely of cavalry for sieges.

Counter spears with sword or axe-wielding forces. The more armoured, the better, since u dont need speed that much fighting spears.

I used this strategy all the time in RTW, it might work in MTW2 as well.

If you've breached a wall at multiple locations, first rush two, maybe three units of your crappy spearmen into the streets at the leftmost or rightmost breech.
Put them in guard mode, and wait till the enemy sends their superior infantry to attack them.
Then send your heavy cavalry through one of the other breeches, and attack the enemy infantry in their back.

As for defending sieges, you should try to pull of the same thing: pin with your own spearmen, and have cavalry attack in their back. They'll likely not get a charge bonus due to the lackluster pathfinding (in RTW at least), but they should win.

If you're heavily outnumbered this will probably be extremely tricky.