I would say for one modders would have much more information on the base to work with.
I think in many cases a bigger issue is going to be how the game is designed, whether open or closed source.
If your open source game is a mess of poorly-documented, barely-decipherable spaghetti code, held together by a bunch of tacky bullshit, that’s going to be a nightmare to mod.
On the other-hand, a closed source game may have absolutely phenomenal documentation and tools available specifically to enable the modding community.
Similarly, you can have well-written, open-sourced code with built-in mod support with proper documentation, and you can have ridiculous bullshit closed-source code that no one is quite sure how or why it even works.
Then again, Minecraft used to be (maybe still is? I haven’t modded in a while) a big mess of spaghetti code but somehow modders not only made it work, but made it work without any documentation and working from obfuscated code.
If anything, modders showed Mojang how it’s done. Looking at it now, the Forge API is really familiar
