How does that imply that slavery was better? It doesn't. It's an insensitive thing to say, sure, but that's different from saying that slavery was better.
That statement was placed in the pledged to make a negative comparison to the Obama administration, therefore it made a clear implication about slavery. Really, what was the point in even bringing slavery up?
If you choose to read the statement one way that suits your views, that's fine, but don't accuse anyone of not being factually correct. Thank you very much.