Which is weird, considering that in the actual convention itself, northern states like New York, New Jersey, New Hampshire, Connecticut, favored the small state position, and Virginia, the biggest slave holding state, favored the large state position. And I think one of the Carolinas supported the big state position--I'm not sure if it was North or South Carolina. And there was nothing in the convention itself that stated the reason for the small state position was to protect slaveholding.
And it wasn't reluctance to talk openly about it either. After all, slavery was discussed and voted upon in discussion on representation of population and taxes (resulting in the 3/5th compromise), the 20 year slave trade ban, and the fugitive slave clause.
But never was there anything about Senate and the Electoral College about slavery. We have the journal of the proceedings and the debate of the Convention, and it's not a myth about the need to accomodate the small state's interest. It actually happened. There was actually a battle between the small states and large states, and as far I can tell, that's all there is to it.
It might be logical in Amar's mind, but there's no evidence in the Convention that the Southern and Northern delegates discussed the small state large state battle on free and slave terms. Rather, it's best to think of it really a large state small state battle, period.