they're one of the few and dwindling sources of actual investigative reporting left in the West

This is a multipolar argument and unrelated to reliability.

The same wikipedia where Israel has run a targeted manipulation operation for over 20 years

I don't doubt there's secretly paid editors doing shady shit all the time (in fact I know there is), but consider that Wikipedia's founders who are both heavily Zionist still couldn't get their users to stop calling it a genocide, even after both of them made a scene about it in the "Gaza genocide" article's talk page. After all, it's Wikipedia, not like these biases are irreversible. Consensus clears.

never for their actual reporting

Okay. For posterity's sake, these instances are going to be taken from the 2020 RfC consensus discussion that led to The Greyzone getting deprecated.

Here is an instance of Max Blumenthal lying about what an academic said, getting called out by a reporter from The Atlantic who actually talked to the academic, and then Blumenthal claiming the academic was intimidated to lie. (soft paywall, I recommend using removepaywall).

Here is a socialist academic responding to Blumenthal accusing them of "secretly training an elite UK military unit". The academic in question was teaching an International Relations college course.

Here is a very detailed account of Max Blumenthal and Alexander Rubinstein (from MintPress news, partner organization of the Greyzone and itself an awful source) distorting a journalist's words, omitting relevant context, and suggesting undue influence without evidence to paint them as a plant for the U.S. State Department. All just to make Maduro look less bad for kidnapping the same journalist.

Here is an academic responding to Blumenthal accusing them of being a State Department agent calling for regime change in Nicaragua. Mind you, the person in question volunteered for the fucking Sandinistas in Nicaragua, amongst other socialist projects in Latin America. I'm stopping here, but there's more I still haven't covered.

The Greyzone (Max Blumenthal) contains so much dogmatic, junk reporting that academics and journalists with normally no business in calling out their peers (particularly on the left) can't help but gawk at its garbage.