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At what confidence interval?

I'm not asking as a 'gotcha' question, I'm acknowledging that the sample size matters. A lot of these statistics are bandied about without really elaborating on the full context of the way reliability is actually measured in industry.

Without checking for the most up-to-date numbers, I believe the F9 is slightly better than Soyuz on raw numbers (successful flights / total attempted). But Soyuz probably has around 6-7x more flights, meaning we have much more confidence that the Soyuz numbers accurately reflect reality.

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Soyuz has only had 140 flights, and had some non lethal mission failures in recent decades. It’s a manned mission vehicle only though. Overall I don’t think you can really say one is more reliable than the other, they’re both very reliable. I’m just saying the suggestion that SpaceX approach is inherently less safe is very much contrary to the evidence.

Having said that I do think propulsive landing for crewed vehicles is pretty scary. F9 firsts stage landings have been pretty reliable for a while, and they now have several boosters with 10 or more flights, so we’ll see. It’s not like capsule landings are 100% safe either.

>Soyuz has only had 140 flights

There has been over 140 crewed launches. For context, you seem to be counting both test/demo, crewed, and uncrewed F9 launches. Again, I don't know the exact number off the top of my head, but there's probably ~10 crewed F9 launches, so it's an order magnitude difference using the same metric. It's gets better though, when comparing total launches.

> Having said that I do think propulsive landing for crewed vehicles is pretty scary.

Not that many options for landing something that size on Mars. That’s what’s really driving many of the design choices.

This is true -- there is a lot of small number statistics in estimating the reliability of launch vehicles. And there are a lot of small risks you never see until you accumulate a lot of lunches. But that question is completely incidental to the design methodology.

A new vehicle will always be unproven. But one that's flown 5 times in testing (4 of them unsuccessfully) before its first flight will have had more flight time on most of its systems than something like the SLS where you take 10 years to think about what could go wrong and then do one test launch and call it good.

You're not wrong, but it is a bit of a misdirection and strawman. The GP was making a global claim compared to all launch systems, not just SLS.

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