Depending on the market and product, players from either side may win the whole thing or it can stay fragmented. Often, eventually, the enterprise players do try and move down-market by building the muscle for product-led growth and hiring developer advocates while the SMB players try and move up market by hiring sales and building out the product to be more enterprise friendly.
In my own industry, it seems like enterprise companies moving down market are having more success, but I can imagine in other markets the opposite is true. In some areas the customer is so valuable that products can keep being built for them, but that’s an open question (that the author seems to be betting on, for now).