I’ve worked in A, B, and C environments. Having agile “inflicted” upon one can sometimes be painful. In fact, that is how I was first introduced to it. By giving it a chance and going “all-in” I was able to see and reap the benefits - I “became a believer”.
Ideally, support should be both bottom-up and top-down. If a team doesn’t get all the top-down support it needs it makes the job very tough. If they manage to get some wins sometimes this helps to fuel change from the top. In my case, it was ironic because the mandate came from the top, but the true buy-in at that level was missing. It took a very long time to get there but it happened by changing the minds of the leaders rather than the leaders themselves.