"Which is why SpaceX packs nine of them into a single Falcon 9 rocket."
Eh, half true. Yes, Falcon 9 requires several Merlin engines in part for overall thrust. But it's also for multiple engine out redundancy for both launches and landings. Something that has on one or two occasions allowed a launch to continue to optimal orbit despite engine issues during F9's testing and development phases. That's also why the BFR is designed with a good number of Raptors instead of just one, monster engine. You can debate the merits of having as many as it does, but that it needs more than one engine is not just a performance question.
The other important part of the equation is that Merlin was designed to produce an MVP, minimum viable product, in Falcon 1. Falcon 9 was a bit too heavy a lift for a first-pass rocket from a company that had never done it before. So you build a moderately powerful engine to get the skinny stick to orbit, then pack a bunch of them on your bigger stick instead of building out a brand new engine for each scale of rocket.
Not saying the article is straight up wrong, but it's somewhat necessary for the "singes Musk and SpaceX" thesis. BE-4, New Glenn, and Vulcan are all threats to SpaceX, but they are over the horizon threats, not current ones. And the threat certainly has little to do with how much overall thrust the engine puts out, because that's a design decision more so than a measure of a company's competitiveness. What IS a measure of their competitiveness is that they are able to get the engine to a hot fire phase and book an established customer to put that engine on their next gen rocket. SpaceX will be watching what happens with BE-4 very closely, to be sure. But I highly doubt anyone in Hawthorne is particularly nervous or bothered by this. Not for another 2-3 years, anyway.