Sea Dragon was the king of paper rockets. It was founded on a sound principal, things get bigger faster than they get more expensive, but he extrapolated an ultra-cheap engine design up to a level FAR beyond what is actually possible.
Starship today is currently taking advantage of the two fundamental things Sea Dragon actually had right, which were A: make your vehicle as simple as possible to construct, and B: bigger is better. SpaceX could ave, for example, stuck to carbon fiber BFR and not even be close to where they are by now in terms of development progress, or they could have switched to steel and fast prototyping etc but only gone from a 9 Merlin engines rocket to a 9 Raptor engine rocket, an improvement but not industry-shattering. It's the combo of size and low cost construction that makes Starship a successful architecture, so long as they get it working of course.
One thing Truax got dead wrong was the idea that more complex engines would always be about as expensive as they were at the time. It's true that back then an F-1 was actually cheaper than a cluster of 9 Merlin sized engines would have been, but nowadays that's not so; 9 Merlin engines cost less than $5 million, and offer both a higher efficiency and thrust AND thrust to weight ratio compared to a single F-1. Raptor is looking like it's gonna be about as cheap as Merlin due to economy of scale manufacturing, which would make it even cheaper per unit thrust, with much better Isp and reuse characteristics. That's another thing, back in Truax's day they weren't even thinking about large reusable rocket engines yet, and the complexity and cost at the time made it seem like an easily reusable high efficiency engine would be pretty much impossible (even the RS-25 which came about a decade later and was designed for reusability ended up requiring massive overhauls for decades before they got to the point that they only rarely needed to replace parts). Hence big pressure fed chungus.