It worked out in the end, but I can’t imagine being so confident in a new system, no matter how much money and brainpower has been spent to make it safe.
That's undeniably true. Nonetheless "Better than the shuttle, which sucked" isn't the design goal.
The question is not even just "is it better to blow up 12 Starships?", which would probably still be true. It's "Why isn't Starship working yet?" and the implied "Maybe Starship sucks too?!".
'5 times as long' is dubious too. SpaceX claims to have been working on the design since 2012 vs 2011 for SLS. Ultimately though the start date of a complex program is not well defined, as early conceptual design stages can take years without leaving the drawing board. Government needs to put a start date on such efforts for legal/budget reasons, but a private company does not.
Also relevant - SpaceX has been given a lot of tech and expertise from NASA at a tiny fraction of the cost and time it would have required them to develop it themselves. Therefore, the costs of NASA programs like space shuttle actually includes some of the development costs of SpaceX.
Both programs pale in comparison to Saturn V, which was faster, cheaper, and more technically demanding at the time.