What leaves me frustrated by pieces like this really amounts to: in practical and literal terms, what do you want Lorne Michaels to do? Because it kind of sounds like you want him to apologize for existing while slowly lowering himself into a vat of acid, live on television.
To be clear, I have always sort of assumed that Lorne Michaels is a crazy asshole who I would not enjoy spending time with. However, my strong suspicion that he's also a savant at picking talent has been repeatedly reinforced by listening to Dana Carvey and David Spade talk to former castmates on their Fly on the Wall podcast. (which is great listening, btw)
There are always going to people who are pissed off that something they don't like appears to be working better than anything else has, before or since. This essay is that. I would bet real money that the author would accept a cast role if it was offered to them; a sort of cynical "hate the game, not the player" shrug.
As for Seth and Tina not speaking out about Sanz: I have a hard time imagining either of them holding back if something was upsetting them. To me, this suggests that perhaps they know (or believe) something that the author of the essay doesn't.