Realistically, there are a handful of modders who are comfortable making .dll mods for the civ series, but .dll access allows them to add new functionality in a way that you cannot if you don't have it. This does mean civ 5 has some areas where you can mod it effectively in a way civ 6 cannot be modded - AI is one which comes to mind; Real Strategy is great, but the small amount of civ 5 mods that were able to use the .dll level modifications were able to re-write the AI; Vox Populi basically re-wrote whole chunks of the AI again, is my understanding. Real Strategy can still use Lua to have more intelligent AI - that allows for additional logic to be added and some existing logic to be changed, but with limitations. In that way, civ 5 is more moddable than civ 6 - however, there are literally a handful of mods that have done this level of .dll work in civ 5's history, at least to my understanding. It took a very long time for most of them to be completed to the standard they're at today, and in general it adds limitations. Limitations in terms of what mods get made using them - they tend to be larger collaborative efforts to share the load of the C++ work - in terms of what level of flexibility the user has - you cannot have two .dll mods active at the same time - and in terms of who can use them - as soon as it's a .dll mod, MacOS and Linux users can't use them (without emulating Windows at least, which is a big barrier for many people). Civ 6 also has a much wider amount of customisation available within the Lua/xml framework than Civ 5 had - at the most obvious level, multiplayer mods work which never used to be the case. I can remember having to manually hex-edit the Civ5 executable and send it to my friends so we could get a few mods working in multiplayer, and that difference is pretty tremendous in Civ 5. In general, fewer things are hard-coded and need the .dll access to change, which is absolutely a change in the right direction for modability. Once can dismiss those modders who aren't making C++ mods with .dll access as "surface level modders", but that's pretty clearly the overwhelming majority of modders, so making the game more accessible at that level is meaningfully an increase in moddability too. Civ 6 is more broadly moddable than Civ 5, but is less deeply moddable than Civ 5; depending on your preferences, one may seem better than the other, but I think it's unfair to say that one is more moddable than the other.