I like focusing on the root motivation. I haven't been able to get to it based on previous conversations. It seems to be perceived velocity because of the increased visibility from what I've gathered but the fact that we don't even have the option to experiment leads to a bigger issue IMO. The teams just aren't empowered to adjust course.
See if your manager knows what's going on. They may be just as oppressed as you feel!
And they may be willing to go along with smaller secret team-level experiments. Maybe Kanban will result in even better visibility and performance! (And satisfaction)
Yeah, unfortunately I did and have been declined several times to experiment. I've also suggested Kanban too since it feels more in line with the pace and the lacking requirements and also shut down several times.
Do the experiment at the smallest level possible. And if not, it's time to suck it up or find a new job.