What are disadvantages of this [the 5 steps] framework?

A "disadvantage" could be some people thinking it's gonna be overcomplicated and prevent you from going ahead. I'd refrain from sharing you're using 5 steps and just do it. They are really simple, just good meeting practice in my opinion:

1. set the stage (focus on purpose, team temperature check)
2. gather data (what are we looking at)
3. generate insights (so what do we make of the data? How can we work more effectively?)
4. decide what to do (now what can we put in place? What's a next step?)
5. close out (ensure clarity on next steps and get feedback on how this retrospective was)