If you have unskilled people who work poorly together, no amount of process will save your projects.
Peel back the facade of rigorous methodology projects and ask why the project was successful, and the answer is people.
A methodology's weight is a product of its size and ceremony.
Process is not a substitute for skill.
The best way to get a project done faster is to start sooner
If you find that your organization can't make the hard decisions that Scrum demands, then high-risk, uncertain projects have very little probability of success in your organization.