I might be wrong, but I think I'm seeing two basic concepts being tossed about. One is where the GM prefers a rich setting and the other being a smaller setting for the room to express individual vision. I've been doing table-top since the eighties in about every system you can imagine and done a LOT of world building. In either case, you (the GM) will need to invest a lot of time and effort either researching the pregenerated material or inventing it whole cloth. I have two of my regular players who want to GM but refuse to put in the work to prep. It's frustrating since they have these huge, rich, and inventive stories and settings in their heads. It's my hope that before I die of old age they will pull the trigger and share their insanity.
As to the original thread question; The published setting for Fantasy Hero is 'ok' in my opinion but isn't really offering anything I havn't seen in other settings who's writers put in a lot more work and content. Speaking for myself, I can't summon an argument for why you should use their setting over, let's say converting Toril and just using the literal Gigs of content present.
I guess it all boils down to what kind of game you want. The 'least' amount of work is to take one of the larger settings as you wont have to invent as much. You will however have to be conversant with the large body of work, which is a bit of reading generally. Doing something new is less reading but more mentally taxing as you're creating. It's a crapload of work either way in my opinion.