2/ For SolarWinds itself, the password is one tiny step along the way. I can guarantee you that having that password won't allow you in any way, to deploy persistent malware on developers's machines (first you'd have to work around Windefender) and getting knowledge of the company's architecture, its internal Repos, etc. You'd have to bypass MFA too at some point, which the attackers did.

3/ If having malware than monitors developers VisualStudio console in realtime to inject a few lines into it so that it gets secretly compiled into their day-to-day work, without breaking the project, while also providing C2 capabilities; if that, is not "sophisticated", i'd be curious to see an example of "sophisticated" malware.