Hi,
By the time OS3.0 appeared, you needed a Mac way larger than the basic Amiga to run Mac OS, and it´s multitasking was very poor.
It is unfair to compare WB3.0 with windows 3.1, because it was older. It should be better to compare it with Win95, and this one is bigger, slower, requires more memory, and it´s multitasking still was way inferior.
I believe if development of Amiga Os could keep up with Mac and Windows we would have a system around 100Mb or maybe 200Mb, mainly due to extra tools, and better graphics. There is no need to waste more than this to look cool, as Aros has proved :-D