Hercules cards were extremely useful, but in the case of PCs, support meant little more than “if you plug in a card, the hardware will provide it power”. That worked if the cards didn’t happen to fight over who owned which interrupt or which memory region. It was up to individual applications to detect the presence of the cards and to write to them.
In contrast, the Mac II supported multiple displays in the sense that QuickDraw would happily draw graphics across monitors, switching color depths along the way, without applications needing to even be aware of the presence of multiple graphics cards.
The Mac also supported having multiple identical graphics cards plugged in. In contrast, a Hercules card could coexist with a VGA card, but not with a second Hercules card, for example.
You're imagining the fighting of resource ownership issue. VGAs don't even use an interrupt line. It was a simple matter of the Hercules emulating an MDA which had a distinct IO space from VGA/EGA. So you could just slap a Hercules card into a VGA machine and start running software that supported the combination.
I don't know anything about Macs but I have no trouble believing it was superior.
The PC was incredibly primitive in this area. But that's also why there was essentially nothing to configure when you inserted a VGA and Hercules card into a machine. Their physical configuration is defined by their respective standards, and the standard didn't consider multi-monitor support. It's just fortuitous that Hercules/MDA and VGA standards didn't collide.
In contrast, the Mac II supported multiple displays in the sense that QuickDraw would happily draw graphics across monitors, switching color depths along the way, without applications needing to even be aware of the presence of multiple graphics cards.
The Mac also supported having multiple identical graphics cards plugged in. In contrast, a Hercules card could coexist with a VGA card, but not with a second Hercules card, for example.