>>11005082In theory, if I'm not mistaken in practice the full flow staged cycle delivers this same quality in a different way. By having both turbopumps and both preburners running fuel and oxidizer rich respectively while you are still having to cope with high pressure the thermal load is much reduced by the relatively low amount of actual combustion going on inside the preburner chambers. This is good for longevity because so long as the pressures are within the tolerance limits of the preburner and turbomachinery's designs the (relatively) low temperature means that those metals won't undergo any fundamental changes in their structure and as a result they won't weaken substantially with each use. However even if the BE-4 is more long-lived, Raptors are cheaper to manufacture (2 million compared the the BE-4's 8 million) which means that once SpaceX starts putting out the production Starship Raptors with their 300 Bar chamber pressures (giving them 52kN more thrust than a BE-4), even if the Raptors live only 25% as long as the BE-4 they'll still be providing essentially the same amount of raw power per dollar spent to build them, ignoring that Raptors are substantially more efficient and their parent vehicle will launch substantially heavier payloads.
From a purely technical perspective I don't really see any upside to the BE-4 here, in pretty much every category some other engine excels in at least one or more performance characteristics compared to it. Maybe it's because metha/LOX is such a middle-tier propellant choice, maybe any engine you build to use it has to be highly ambitious in it's design to excel.
