Yeah, basically that. I’m back at work in Windows land on a Monday morning, and pondering what sadist at Microsoft included these features. It’s not hyperbole to say that the startup repair, and the troubleshooters in settings, have never fixed an issue I’ve encountered with Windows. Not even once. Is this typical?
ETA: I’ve learned from reading the responses that the Windows troubleshooters primarily look for missing or broken drivers, and sometimes fix things just by restarting a service, so they’re useful if you have troublesome hardware.
The trick to a successful DISM though is matching the broken system’s patch level with that of the source files. DISM basically repairs your component store using the source, so for it to work properly, you’d want to use the same OS patch level store as the source. I used to keep a few good Windows VMs at different patch levels for this purpose. I’d then patch the VM up to the same level as that of the broken machine (if needed), and then use the good VM as the DISM source.
In any case, if DISM keeps failing, then a repair install (aka in-place upgrade) usually does the trick.