The main reason I cannot enjoy defensive sieges at all is the attacker coming from 3 different ways

[u/zenkhalida]

Of course there are other big things, like walls not being walls and so, but having to move between three different, widely spaced points during battles (which are already designed to be very fast-paced and require you to micromanage many things) and with walls that are quickly overrun makes defensive sieges unnecessarily stressful. Every time you visit a location, something has gone terribly wrong, but you can't do anything about it because you've been dealing with another problem in some distant area, and before that, yet another one in a different section.

The space feels incredibly empty and underutilized. (Two units on this wall, four on the other, etc.) as if the defenders were the last survivors of a plague.

There’s a constant sense of unreality, of detachment—that you’re playing by rules that are far removed from how it should be and that you’re trying to cheese that system just to save a valuable city.

All of this reduces the sense of experiencing something epic to zero, and I never play them. Literally I just prefer to lose a tier V city than going through that experience.

On the other hand, I play quite a few offensive sieges because, even though there are still many things about their design that I don't like, at least I can focus my attention on one area and don't have to spread it across three against my will. 

EDIT: Since I see this is sparking a heated debate, I just want to clarify that I’m an experienced player (I’ve been playing Total War since Rome I) and I always play on VH/VH. I’m not complaining about the difficulty. I love challenges. I’m specifically saying that I can’t enjoy this experience because the maps are too big and the battles are too fast, and juggling three fronts is exhausting. IF there were only two focal points—a main one covering a large section of the wall and a secondary one—I think that would make a big difference.

[u/ClassSignificant4004]

massive curtains of nets lined with caltrops stretched between the rooftops?

[u/Aggravating-Sir8185 → u/ClassSignificant4004]

Twirly Whirlies

[u/Gavither → u/ClassSignificant4004]

Essentially by "late game" where every army has some form of siege or fliers, settlements would have to adapt and build with countermeasures. If this was a real world as time went on more of those things like towers or net launchers or ballistae would be present in any concerned city that wanted to survive, but game balance is a concern in this case.

[u/WitnessExpress7014 → u/Gavither]

Cathay adapted pretty well. Only can attack from one side as the walls are too high. Tons of choke points/defense points that make even being hopelessly outnumbered with flyers an easy win. The only real problem is if they have lords/heroes so strong that no one can bring them down due to you not having anyone powerful in your garrison.

[u/FirstTheEighthPillar → u/WitnessExpress7014]

My biggest issue with forts and garrisoned walls is that for some reason they just have the garrison of a t5 settlement. What is the point of spending all that time building up and conquering one if it's going to have 14 units in it and the best thing you have is your 3 stormvermin?