You can do it with plenty of leg space. More so than a table because islands are higher and the seating, unlike fixed chairs is adjustable.
One of my friends is about 6 stone over weight and she sits for hours happily. Basically we have adjustable height chairs. But yes, if you get the wrong seating it's very uncomfortable. The tiny backless stools are shit.
We use our actual dining room as a second living room, because we don't have formal dinner parties and if we did the room would be largely unused. As a second living room it's used daily. We don't need two dining areas.
The kitchen island is where our friends congregate and like to sit chatting (and drinking) even when I try to move them on to the living room. It's a social space.
I think it's important to use the rooms in your house for the way you actually live, not how you think you should.
Our island is large, but my friend has a very thin breakfast bar. Six round it max, and we also sit there predominantly. She has a large dining room table and we seldom eat there. We use the breakfast bar. However she has similar seating to me, and it's comfortable and stable.