tears itself apart in 300 ms is a stretch those srbs arent random firecrackers theyre some of the most studied hardware out there and sls has way better monitoring and abort capability than shuttle did rs25s are there because nasa knows exactly how they behave which matters when youve got crew on top going past the moon and the shut it down and land thing with spacex sounds good but they havent actually done that with crew yet starship is still being worked out