I think the biggest difference was power.
Silco had the power in his dynamic with Marcus, or at least made sure to give the impression he did. He made it very clear he'd kill Marcus's daughter if he ever stepped out of line, in addition to cutting his payroll. Marcus worked for Silco, Silco didn't work "with" Marcus.
Meanwhile with Vander and Grayson, it was the opposite. On paper they were working together, with Grayson keeping enforcers out of the Lanes and Vander keeping Lane residents from committing criminal activity in Piltover. But, the thing is, even before the kids rob Jayce's apartment, we see enforcers in the Lanes, like in the Enemy mv. Grayson is not upholding her end of the deal and there's nothing Vander can or will do about it, but the second he falls short of his end, a reign of terror is brought down upon his business and community. He, in absolutely no way, had any control over the enforcer presence in the Lanes, let alone all of Zaun.
There's also the added element that the Lanes were just one district of Zaun. Vander wasn't even attempting to act "for the greater good of Zaun," he threw the entire rest of his city under the bus in order to keep his own community safe. He didn't care if Silco terrorized all of Zaun with drugs, "Just spare the Lanes." He didn't care if enforcers violently oppressed everyone else in Zaun, as long as his deal caused them to (kinda) leave the Lanes alone (as long as they don't step one foot out of line).
Now, let me be clear, I like Vander, and I don't think he's a villain for this. He was a traumatized man who was terrified of losing anyone else he loved and did whatever he felt he could to prevent more loss. Silco's approach to independence and leadership is also obviously extremely flawed, this isn't to put one down or uplift the other, more to point out that their situations vis a vis working with enforcers were completely different.