The GC role is unpaid, at least directly by EA/Maxis. Whether you consider getting the pack free as payment is up for debate.
The earnings from being a GC come from the audience clicking on streams/videos/posts etc that are done with the pack in question.
Usually, they also get access to the pack early by way of Sims Camp (for expansion packs) where they can point out things that can still be fixed pre-release. Since they probably do that in-person to devs then, we don't get to see it as we did now when Sims Camp was remote - the GCs made a point of saying it was a pre-release build so not everything worked the same way.
As for "more bugs than before", that's debatable, since not every bug affects every player. And the more packs there are, the more likely they are to weird out depending on the combo.
Honestly, I don't think GCs and game testing - the technical side - should be merged. If anything, it would be great to have a larger QA/testing team and maybe a more extensive and more accessible playtesting program (right now, if you're not in the right country, you're out of luck). QA is a big job and while there are people who'd be willing to do it for free or just for free content for their games, it's probably not a good idea to set that precedent.
(Signed, former software tester whose job was worth a regular wage)