Back in the 80s/90s, AmigaOS was a lot more efficient than DOS/Windows, and even MacOS to some degree (Macs couldn't really get far without a hard disk, for example). So this claim isn't just comparing to modern machines.
I'm sure if Commodore hadn't gone bust, modern Amigas would have higher system requirements, but obviously it's impossible to judge something which never happened. OS X isn't even the same OS as Mac OS of the 80s/90s anyway, so one can't really say that Mac OS grew more bloated, rather Apple ditched it for another OS. Who knows, if Commodore hadn't gone bust, modern Amigas might be running the bloated Vista... (I believe the plans for next generation Amigas at one time included HP Risc machines running Windows NT?)
