Actually copyright retains with the original author even its you do no own the IP, i know someone that had to deal with this

involving a comic that was using his 3d model and rendition of somthing and the comic even though they owned the IP had to remove it.
That sounds possible, but it doesn't mean that "if a person made something it automatically makes it theirs." You'd have to clarify how the publisher of the comic had acquired the 3d model in question. If it was obtained inappropriately then yes, they would have been stealing the persons property. Even something as questionable as: the person having been a contractor who produced the model under the terms of a contract, which had at some point been breached by the publisher, could be a sufficient basis for the artist to press for the publisher to remove the asset from their IP (depending on the specifics of the arrangement).
This can never apply to things made as part of a "modification" to a game (unless it is specifically written that way in the EULA, a specification of which I have never heard). Publishers of games that are open to modding are essentially allowing users to make content for their game. It would be extremely problematic for them to specify that each content maker is the owner of their content, or to specifically allow this, because this would in turn give them absolutely no oversight over said content, and it could put their own IP at jeopardy.
Lets take Minecraft as an example, and say that I make a bunch of cute little models for that game. They turn out to be very popular, so I decide to make T-shirts (or comics, or coffee mugs, whatever) and sell those products. Microsoft sees this happening but because they wrote the EULA the way you think it operates, they are powerless to stop me from making a profit off of their game. It get's worse from there: Sony sees that I'm very popular with my "cute Minecraft Bunnies" thing on Youtube, so they offer me a $10,00,000 contract to produce 3 seasons of an animated cartoon series with the bunnies. Now we've got two firms whose intellectual property is overlapping and at some point the lawsuits are going to start flying. This is not the way it works: firms that sell games, to my knowledge, never give ownership to creators of "modification" content for their IPs and in fact always specify that they have sole and final oversight over said content. This could go so far as to mean, they can commandeer your creation and sell it, but as far as I know that has yet to be contested in court, though it has been "discussed" by some publishers.
That would get really awkward if someone were to apply the same model across multiple games. Then suddenly multiple companies can claim ownership of said asset.
Possibly a reason why ownership is still retained by the original creator for assets.
Coding and syntax are a different story since that's a genuine product from Paradox itself.
"Coding and syntax" is a bit obscure there . . . C++ has syntax, so does Java, Python, etc., etc. The fact that it has "syntax" does not mean that I own Bjorne Stroutroup royalties if I make a game engine that uses C++ or that I owe Sun royalties if I make a mobile app that uses Java. This area can be contentious, it is true and some "language publishers" retain copyright over their language, SAS for example sued some folks in Europe some years ago who were using their language to write their own software. SAS is not something one "writes applications" in though and it is the only one I'm aware of that functions that way; it is essentially a command language for running a combined RDMS-statistical analysis and graphical application. Companies pay big bucks to get licenses for the package. Most programming languages are not copyright as far as I know.
However, a "package" of functioning programming language can be proprietary, and as long as the creator of it is careful about how they release it (e.g., if you put all your stuff up on Github where anyone has access to it, then years down the line try to sue somebody cause they made money off of code you wrote, you probably have a serious up hill battle in court). This is why you'll notice that source code for functioning software that is not open-source is very, very rarely released; it is essentially the secret recipe and by keeping it private, a publisher places themselves into the "de facto" sole possession of the IP which will give them the greater leverage in court, should it ever be contested.
The moral of this story is quite simple: if you truly want to have "ownership" of any piece of intellectual property than you make, then (a) do NOT base it on the work of anyone else, particularly a firm that sells products that are based on their own IP(s); (b) do NOT share it with ANYONE (not even your mother!) if they have not signed an NDA and/or other agreements specifying that you are the sole owner of the material in question; (c) when and if you do release, make sure you've consulted with an intellectual property attorney first.
Because, at the end of the day, a skillful hacker can get hold of anyone's source code (much less assets that are not compiled into machine code in their final distributed form like graphics or scripts), and you do not want to be in an ambiguous situation where you cannot demonstrate that it was your's to begin with.
That happened to the guy on whose game Perrson . . . "based" . . . Minecraft.