Wholesale and dropship are two different business models. Please do not mistake the two- especially to new online retailers.
Buying in wholesale means meeting the supplier's minimum order requirements (either by the case or purchase amount) to get the wholesale price. The more items or case quantities you purchase, the cheaper your wholesale price is going to be. Dropshipping typically does not have dollar/ order minimums- meaning the dropshipper can process and ship your single unit order to the end consumer.
Seeing the difference between the two models' order requirements you can expect that the wholesale price is going to be cheaper compared to that of the dropshipping price. A retailer buying 2 dozen cellphone cases will acquire a lower purchasing amount as opposed to someone buying one (1) cellphone case.
The profit margin is not the greatest "strength" when it comes to dropshipping. However, this business model is still going strong is pursued by online retailers. Why? Technically with dropshipping there's not much capital you need because you only pay for the products you have already sold. Start up costs vary depending on where you want to list your items and if your dropshippers have any membership fees. This allows you to explore different target markets and which one works for you and your business, and which one doesn't.