You sweep a foot with weight committed to it, not weight off it. If you are messing around with weight on feet you will just be moved around, pulled onto a foot, and swept or tripped by a decent grappler. If you are standing on one leg with no weight on the other foot then you present a huge osoto gari opportunity, with horrible fall and back of head to floor ko very likely.
This is a non argument. Heel vs toe is talking about a committed weight foot. Toe is better vs sweeps and trips because musculature engaged and easier to react, not fool proof though of course.