The devs picked the ability to give lots of freedom to mod developers to do a very wide range of things over the convenience of it being easy. The modifier system is a great example of this, it is rather cumbersome to use but has opened many, many doors for modders that were simply not available in previous versions. Whether that is a good or a bad thing is subjective, but there are ~1000 mods on steam workshop which suggests a fair number of people can do at least basic mods.
As for getting a 3d model to work, this is not so bad. Creating genuinely new art is hard (and requires the pain that is Blender) only because creating 3-d models of stuff is intrinsically difficult. If you just want to combine different existing models together or recolour them: say, give cavalry a musket as a weapon and make their uniform yellow, it isn't too bad. There are some guides on the forum on how to use ArtDefs and it can be done fairly quickly.