That's some impressive commentary, and completely arbitrary. Can you take business away from other companies in saturated markets, sure, if you have the right technology, Amazon did. Can a website self-market, sure if you've to a high LTVtoCAC like Amazon (15to1) compared to everyone else (3to1 to 5to1) and use the right tech. Can you do that with Shopify, no, can you do it with Magento out of the box, no, can you do it with Hybris, not at a realistic cost, can you find developers who know how to compete in that market and understand pure efficiency outside of enterprise companies, no.
Ok, we know them and yes it'll cost £10,000s but here's the simple point, to beat a saturated market you need to be more efficient than your best competitors, and to be more efficient you need more efficient implementations, not taking months but ideally weeks, it makes your entire business model agile and lean. Amazon did it by building their our technology but that is a sunk cost over a multi-year period, we know people who did it by stripping out all the rubbish in existing technology again as a multi-year sunk cost, most will just build on existing technology making it more inefficient as there is no material short term sunk cost, that cost is spread over the business lifetime which is what makes the business inefficient, which leads to complete failure in core markets.
Unless you have £millions in seed capital only the first two will work, the last one will just be a slow, or perhaps fast, road to paying providers to build something which has no hope of making you sustainable and business adapting revenue. With 1,500 products it's too small, if you want traction you want 10,000s products, only a small fraction will make the profit but the rest are there for 'show' for Google and potential customers benefit. Look big, act big, work lean, work efficient, and people will think you are the go to place. The smart entrepreneurs these days start with a Lean Startup methodology and incrementally build on each success, unfortunately you're not going to find many providers liking that approach.