On the Topic of "Modding Friendliness", I agree with People here in that Civ VI is a very moddable Game, not just compared to Civ V.
Yes, we don't have access to the Gameplay DLL Source Code, but a lot can be done even without it. Civ6's Modding Capabilities are really great and offer a lot of Possibilities, but they also have some limitations:
is better than in any previous Game, and opens a lot of Possibilities that previous Titles didn't offer. Allows for changing Appearance of many Models based on Era/PlotProperty/Ability..etc. adding new VFX, changing Game Lighting (@pokiehl
just recently made 2 Mods that change the Dark/Gold Age Lighting), access to most Assets in the Game that we can reuse, combine and reskin as we want...etc.
unless you're just resung Game Assets, it can be a tedious work to use the Asset Editor Software (prone to crashes), and adding new custom Models. We can't add new Terrain Types
with new Graphics.
Since NFP, the Asset Limit Bug proved to be a big restriction for adding new Assets to the Game, so eventhough Graphics Modding is great, we can't make full use of it, which is a big waste.
The Modifiers Systems is basically Database Scripting that allows modding the Game with only xml/sql, without requiring to have any programming/scripting Skills. It's easy to use, MP stable/compatible like @pokiehl
said, and very flexible in that you can mix and match nearly every Effect and Requirememnt in the Game to make something new. And nearly every Mechanic and Parameter in the Game can be tweaked/balanced. Not directly related to DB Modding (alone), but the Modinfo of Mods allow for a very flexible way to ensure compatibility with other Mods and adding various Game Options based on any Game Settenigs that you want.
A lot of things are hardcoded, and many Effects/Requiremnts only work for specific Things/in certain Environments.
A big Lua Library with Tons of Events, Objects and Methods. Allows to greatly expand the Roster of Database Effects/Requirements within its own Environment, and using dummy Buildings or the Plot Property Methode even allows to add any kind of requirements to the Database, which in combination with the Modifiers System opens the Door for practically controlling the Database Effects with lua. Technically it's possible to mod/control the AI with lua (to a degree), though without doubt it's a lot of Work and workarounds to do that (and may take a lot of processing Power, even for lua). Allows adding new Mechanics to the Game, or even change existing ones where possible (especially in combination with the Modifiers System). May also be used to fix many Bugs. Offers a greatly moddable UI.
: The lack of a proper lua API (and Database) Documentation proves to make lua modding a very time consuming task, making you lose a lot of Time just with testing things. The destinctions between Gameplay and UI Contexts is very annoying, because a lot of Objects/Methods either work in one Context or the other, forcing Modders to find other ways to transfer data between them, but with Risk to cause MP Desyncs. The lack of many AI Objects/Methods (especially for Diplomacy, Empire and Unit Management) puts a hard limit on how far you can go with modding the AI, especially when adding new Game Mechanics that you want the AI to make use of. Since many Game Mechanics are hardcoded, and can only be tweaked to a certain degree, reworking them isn't possible without coding them from scratch.
Personal Experience with Civ6 Modding:
I've been working on a Game Overhaul Mod since over a Year now myself (see my Signature), and from the experience I gathered from that (and since I started modding the Game), I can tell you that making Total Conversion Mods (like Rhy's and Fall) is definitely possible, even without the DLL, and even AI modding is possible to a certain degree (if you're willing to make some sacrifices in making designs that take AI under consideration, spend a lot of time scripting AI behavior from scratch or adding Mechanics that help AI decision-making...etc). So, even things like fixing AI not improving Resources and building Industries/Corporartions, and fixing the huge Monopoly Bonuses are possible, if you're willing to take the time for doing it. (which is also one of the main reasons why my Mod is taking so long)
I don't know why most Modders stack with Civ IV/V, and didn't give Civ6 a chance, but the lack of a DLL can't be a reason for saying that things like Total Conversions and new/reworked Game Mechanics aren't possible. Unless one wants to mod every Idea that pops into their mind or prefers C++ to mod the Game, we have to make some sacrifices and accept some limitations, and tbf, exactly that helped me a lot to learn and understand Game Design and to be creative in how to accomplish things (Workarounds can be very rewarding ngl), and I think it even helped my Mod to be much better than if I had used the DLL to mod it.
Civ VI Modding is really great, we can balance and tweak nearly everything very easily, add any kind of Content, add very unique Abilities, introduce new Mechanics/features to the Game, fix many Bugs were possible, and also allows for making Total Overhaul Mods. But a lot of things in the Game are hardcoded, and require access to the DLL in order to change them or add to them (Like Espionage, Trade Routes, Specialists...etc.). The Asset Limit Bug is also a big detriment for People who like to use Mods that add many new Assets to the Game. And since Firaxis didn't expose many AI lua Methods, it's really hard to mod the AI, it's not impossible, mind you, but not an easy task, to put it mildly.
Nevertheless, a lot can be achieved without requiring the DLL, in fact, I wish that Firaxis will double down on the Database and lua moddability in Civ7, have less hardcoded Mechanics, and make AI scripting with lua possible (a lot of Games use lua to script the AI anyway) + SQL Artdefs and no Asset cooking this Time please!