I don’t know if that is actually true, if you look at what’s actually going on. At the start of the game, when most things are minimum level, especially at 867, it can definitely feel like it’s true - any low-level castle is going to take less than 5 months to siege, and if you’re in tribal areas, you’re not even up against castles, just pathetic fortifications, but as castles get higher level, the siege times get extremely long, especially if you don’t have siege equipment (which most people don’t). For example, by 900 AD I was seeing rare places with took nearly year to siege, even with a big army, and that was a serious problem.
Terrain can be very significant, too. I defeated a much larger army a while back because I engaged them in mountains, and had more elite troops - in the open field I’d have lost for sure. The penalties for doing stuff like crossing rivers can be pretty harsh too. It doesn’t necessarily mean you’ll lose a battle you’d otherwise win (maybe it should, but it does)
Wars aren’t “realistic”, sure, but if you find me a futuristic or historical (outside the 20th century, which seems to be the only thing people approach in an even arguably realistic way) strategy game that has “realistic” wars, then I’ll be very impressed. I’ve literally never seen or heard of one. I’m racking my brain and I can’t think of one. I can’t even think of one that is just “more” realistic than CK3, because they’re all extremely unrealistic (including CK3).
If it was realistic, about 90% of the game would be rounding people up to be your soldiers, trying to keep them fed, preventing them from running away before and during the battle, keeping them together, keeping them on mission and so on. CK3, unlike most historical strategy games, makes at least some effort to simulate most of that, even if it’s a cursory one. The least realistic thing is probably how powerful knights/champions are in the early game.
The main issue with war, from my perspective, is that there are tons of modifiers involved in all the different aspects of the war, and it’s hard to know which is applying and when and how. That and maybe war is a bit too easy for the player.
That said, if you’re an experienced CK2 player, I think it may take you a long time to warm up to it. My wife has like 2000 hours on CK2, and initially wasn’t very fond of CK3, with some of the same criticisms as you (particularly re: map/UI - part of the map issue is that’s about 2-3x as much stuff to potentially click on of course). However, she’s kept playing and has warmed up to it. Personally I find it a lot more approachable. I’ve heard a lot of stuff is “hard to find” for CK2 players, but I think it’s more like it was even harder to find in CK2 (in a lot of cases), but they knew were it was then, and now it’s in a different place, and has to be found again.
Functionally it’s also launching with an amount and detail of material that CK2 didn’t get for multiple expansions.
My biggest complaint would be that the game doesn’t always alert you to important events whilst frequently alerting you to pointless ones. If my capital is being sieged, or my army commander dies (even if not in battle), I’d like to know about it, for example. I’d rather know if a vassal starts a war (especially a son/daughter) than if someone wins/loses a war nearby (which is typically largely inconsequential). I had a 30 martial dude who lead my armies and at around 60 he just mysteriously vanished. No message, nothing to indicate what happened, and if I hadn’t clicked on the army just idly, I wouldn’t even have noticed they had no leader until I put them in a battle! Thinking about it I guess I can find his wife so perhaps I can work it out from there, but still! My favourite mechanic is probably the Stress one, which effectively strongly encourages you to actually role-play your character, rather than just always making the absolutely most rational decision you can come up with.
JE Sawyer is working on a new game with a small team that we know absolutely nothing about, but he was very enthusiastic about Disco Elysium and has talked about making a “non-violent RPG” (which is essentially what DE is) for longer than DE has existed, so there may be some hope there. Of course he’s also talked a lot about wanting to make a squad-combat-level quasi-historical medieval tactics RPG (i.e. Darklands meets XCOM), so that’s in the mix too.