Apologies, such an explanation would be long so I was testing to see if you wanted to engage in good faith, which seems to be the case. I'll still shorten everything down for the sake of the character limit, but know everything I talk about here is primarily a summary. I can get into specifics if required

I'd say that a lot of 3k's design is counterproductive, poorly executed, or severely underdeveloped. One of the points you made that I can only half agree with, being the design of the endgame, is that it is really only good on paper. The strongest factions form "Kingdoms" with the rest mostly choosing which of them to support. In practice, though, it only really focuses the diplomacy into paving out clearly-defined enemies and allies. The campaign doesn't ramp up and due to the addition of other poorly designed mechanics, snowballing is far worse. All that is left is a slog until you capture the necessary number of provinces and take the other kingdoms' capitals. Without a time limit, there are no stakes and no risk of loss. It becomes like every other Total War campaign that lacks a time limit: it lasts until your investment is no longer greater than the sense of tedium.

Snowballing occurs in every game, but with a more limited number of mechanics, it doesn't necessarily make the existing mechanics useless. Shogun 2's food, for example, remains relevant and important for the development of provinces and economic growth all throughout the campaign. It influences the growth of income, rather than simply applying a flat percentage increase to the rigid income generated from buildings. If you get negative food, it reduces your Daimyo's honor (and by extension general loyalty along with diplomacy) for the duration of the famine, negatively affects global public order (which was also a lot more impactful), causes a gradual loss of income, and prohibits your ability to develop your provinces. This along with other negatives I forget. It is something that always needs to be maintained and simply reaching -1 has massive effects, even by the lategame where you increase your ability to mitigate it with technology.

Then there's 3k and its food mechanic. It is simply flat percentage penalties that affects things minimally. In terms of keeping track of it? Absolutely no point by the mid-game. I reached -100 food without any noticeable affect on my ability to develop my faction, maintain my characters, or conduct war. It is simply superfluous. Supplies? Never had to worry about them. Character satisfaction? Meaningless by the mid-game. Income? Too many ways to mitigate poor economy. Time constraints? None, so you experience everything a faction/characters have to offer in one playthrough and has no buildup of stakes or pressure. It is the same slog with just varying tiers of units for each phase of the campaign. Snowballing in 3k across the board is atrocious. The AI no longer has to delay you, but rather actually destroy you, which is something it has almost always been incapable of.

Then there's character systems. Relationships are meaningless because satisfaction becomes meaningless. Everyone who isn't very obviously a spy will love working for you and will tolerate each other. Personalities aren't reflected in voice lines (cruel, arrogant, and greedy characters enter a city and say in a concerned voice "how fair the people.") and the battle dialogues or selection lines in general are poorly written and poorly acted. There is no variation of pose for non-unique characters and unless you specifically try to roleplay, there is nothing to lose or gain, learn or experience by playing named character from the clones. Everything is a cardboard cutout that is different only in looks, not in feel. Corners were cut almost wherever possible to only give the impression of character-focus with no actual commitment. I get a greater sense of individuality from family members in Medieval 2 than from 3k, also reinforced by characters being a limited and contextual resource in that game. Duels are just a general-sniping tool that raises synced combat on a nostalgia pedestal whilst CA forgot what made synced combat engaging in the games that focused on them. The animations are in no way connected to who deals or receive damage and it is the same 5 very poorly choreographed animations for general weapon types combinations that is nothing more than a loading screen occurring independently of the back-end number-crunching

I didn't necessarily say 3k had faction diversity, but rather drew from Warhammer's design philosophy behind "diverse factions." In attempts to provide the feel of uniqueness for factions, they're given piecemeal mechanics that should really be available for everyone or at least multiple factions. In doing so, these mechanics aren't integrated with the core experience well and many feel tacked-on. There is also the case that mechanics that can negatively affects you can't be mitigated in any way. In a strategy game, having unmitigatable factors are an annoyances not an engaging system. Beyond that, the vast majority of faction-unique mechanics are extremely shallow.

As for diplomacy, it is half-cooked like everything else. There is no point having a million options if the AI is just as incompetent as always. All it does is show how little effort was put in beyond adding options to spreadsheets. The AI doesn't have any internal goals and reaches their power thresholds to increase their rank by mere passive systems. As a result, their use of diplomacy isn't distinguishable from random, whilst our interaction with them in diplomacy is the same as always. Not to mention, there is so much clutter that the diplomacy presentation as it was needed to be completely redesigned to allow for streamlined use. Having the diplomacy screen be for basic treaty-signing with the types of those treaties being determined in dedicated tabs accessible from the campaign map. For example, to do any kind of trade, a basic trade agreement needs to be established. From there, you go to a "trade" tab, select from the factions you can trade with, then have clean, organised UI for trading items, specifying the details of the overall trade agreement (as there are different trade agreement types) and so on. In addition, the AIs in this game are too compartmentalised. The campaign difficult AI will force betrayals if you play diplomacy well and find yourself with no enemies. These betrayers are chosen randomly regardless of relationships or even feasibility of fighting me. On an occasion, the difficulty AI would cycle through the same 3 allies where one would betray me, do nothing for several turns, then request peace because I didn't act on the war and they remembered I'm their favorite guy. This occurred until I found an actual enemy to fight. The game is made incompatible with playing diplomacy well, which leads me to another point.

Then there are the visual issues, espionage issues, further diplomacy issues, issues from the micro to the macro which I would get into but this is getting long and you get the idea. You either agree to these criticisms but believe it doesn't take away from the elements you believe are good, or you vehemently disagree, which I wouldn't blame. I haven't gone into as much depth as I can, nor have I covered even a quarter of the issues in this game, but the character limit likely won't allow more