For music, at least, 25% cut is actually pretty substantial. I would negotiate a smaller cut with anyone interested in collaborating. The real question is what standard modders will set their work at. If everyone lowballs, the system is doomed.
In music, you have game developers thinking that music is a hobby, and so their music budget should be 0%. You're expected to work for free, or sometimes they'll say they'll pay you if your work is "high quality." You finish the asset, they say they don't like it, and suddenly you're facing a loss - you can either capitulate and let them use it for free so that you at least get the exposure or go home with nothing. How much is exposure worth to someone that can never get paid work and can never get anyone to do more than pirate their work? This is pretty well standard now for game companies at entry level. There is no inroad without using professional sample libraries considered gold standards at larger game companies, there is no using professional sample libraries without spending thousands of dollars or doing the illegal. There's no doing the illegal without getting noticed, because samples nowadays are watermarked and you face litigation if you ever reach any kind of commercial success.
I might not be part of the 'industry' but I do need to eat, and minimum wage is kicking my ass. This is my only established talent, I've done it for upwards of eleven years (more than that with conventional instruments,) so I'm just supposed to ignore this potential revenue stream because I don't like how much Bethesda is taking? I like Bethesda. I can't even afford to pay for any of their games, in fact I play all of them from my brother's steam library. In my shoes I can't really see the problem here, it's their game, they can make whatever kind of agreements and restrictions on their modding community that they want, and since no one is telling us that we can't not charge for mods, since no one is telling you that you have to buy mods, what possible violation is occurring here?