GP here: there's a couple of key distinctions to be made. Jane Street is operating in a market where there are few off-the-shelf tools, the tools are your comp

GP here: there's a couple of key distinctions to be made. Jane Street is operating in a market where there are few off-the-shelf tools, the tools are your competitive edge, and hence it makes sense to design your own. Similar-but-different tools won't work, at all. The place I worked at were doing the same thing everybody else was. They were making a pre-digital business digital, just like everybody else in the 2000 dot com boom. All the same off-the-shelf solutions applied. The secret sauce was the niche market, legal loopholes, and first-mover advantage. The custom DB vs Oracle thing is a great example. The startup saved no money by developing a custom system, because they had to license Oracle anyway. They gained no scalability advantage, because Oracle scaled to their required level just fine. There's no edge there to be gained over the competition. Worse still, they wasted 3+ years developing their own system, which gave their competition a head start.