
The places you mentioned are drop shipment companies (except for Taka jewellery, which is actually known for poor cuts). Are we going back in time to drop shipments? There are much better ones if you're going the online route like Black by Briangavin or ACA from Whiteflash.
There are reasons why these diamonds are in the drop shipment and why people are trying to stay away from them. All these websites with thousands of diamonds don't carry inventory and sell anything they can sell.
Most bang for the buck equates value, not lower quality.
You can find more and more websites like these popping up everyday, there was once a time Jamesallen used to list up ASET images, Hearts, etc, but they've removed them all.