Never heard about venues taking a cut off the merch - that’s fucked up… They already take (in almost all cases) 100% from drinks and bar sales. In my experience the ticket sales and merch go completely to the artist. Anything else I would consider a rip-off

That is certainly the case with many venues in the US after the LiveNation/Ticketmaster merger. Independent venues are much more rare, due to the LiveNation monopoly, but make their own deals with talent that are reasonable to both parties.

LiveNation operates so much of the venue spaces they can take whatever they want. Artists have been complaining to congress about it since the merger in 2010.

In larger UK venues this has been happening for some years now, there is a campaign against it: https://thefac.org/venuedirectory

This has been followed up by similar action in the US as well: https://weareumaw.org/my-merch