While I think that the cut is not acceptable (imo it should be at least 50% for content creators and 50% for valve and the publisher), I can't share many of the points being made in this thread.
First, the "modding should be free" -> it's bad for the gamers argument:
It still is. You can go to the Nexus and download tons of free mods. You can go to the workshop and download tons of free mods.
Complaining about the content creators getting an additional way to monetize their creations is as entitled as it gets.
Then, the "if this continues, Fallout/TES will ship without unpaid/non-workshop modding support" -> it's bad for the gamre argument:
That's a legit worry, however I really can't see that happening. When Oblivion had that hilariously infamous horse armor DLC, people worried future games woudn't have mod support. A lot of available mods (and I guess quite a fair share of paid ones, too) rely on free third-party dependencies and couldn't have been created, were it not for them. Bethesda will always rely on people fixing their game for free and those patches tend to be incompatible with the way the workshop works.
If mods were workshop-only (and possibly even paid-workshop-only), their next release would either be rock solid (unlikely) or would come crashing down in it's first years.
They'd also would lose a metric ton of goodwill.
Next up, the "content creators are being ripped off" -> it's bad for the content creators argument:
I agree that the cut could be way better. Removing donation links also is a dickmove, yes.
Then again: The workshop is Valve's territory, Valve's infrastructure. If you want to monetize your content using Valve's platform to deliver it while sidestepping the official way of monetization, no shit this will be cracked down on. Some of these mods have a big filesize, you are welcome to build your own mod-platform and pay for that traffic yourself.
Feel free to get a Patreon account or put your donation links on your Nexus profile.
People are actively pulling the content they have provided for free before (see my first point) and migrate to the paid workshop though, so this kind of doesn't seem like it would be worse for the content creators than whatever they had before.
In the end, right now, all of this comes down to irrational fear and entitlement for me.
All in all, paid workshop seems like it would be a good thing for modders and gamers alike, seeing as how people could now make it a fulltime job to create mods.