Here's my take on SLS
I don't think I'm imagining it but I think Elon said after one of SLS's many valve problems "well there's your problem, you have too many valves."
That goes to one of Elon's core rules. Engineers spend a lot of time designing and optimizing a part they may not have really needed. Elon tells a story about sleeping on the Tesla factory floor while trying to solve a production problem causing massive delays. A liner was installed between the battery and the floorboard but they had one helluva time designing the robots to do it fast so Elon spent a lot of effort trying to fix the problem. Then he went to the floorboard people and asked why they needed it and they said they didn't, the battery people said they needed it. So he went to the battery people and they said they didn't, the floorboard people needed it. Elon tells his Engineers to always ask the question is this part really needed? The metric that you are doing it right is that if you have to add parts back in 10% of the time then you are removing enough parts.
One of the big reductions made in going from Raptor 1 to Raptor 2 was getting rid of all the damn sensors it had. They were needed during development but for flight, they aren't needed. The SLS is flying used shuttle engines. The engines been thoroughly tested, flown, tested again, flown, tested again, etc. Then refurbished for SLS and thoroughly tested and fired again. If Boeing doesn't know how the engine performs by now then God help them. The ironic thing is that because the sensor failed and they decided to fly without fixing it means they didn't need the damn part!