Where does the figure of $4k-$6k come from? For many across the world that would still be a large investment. In fact I think the majority of the world's population would not invest that much.
buying whole is a better deal.
This is completely not true, the only difference is psychological. It does not matter if you buy 0.01 btc at a price of 100k or 1btc at a price of 1k. The gains are measured in the percentage growth.