How much your words matter as a senior engineer depend on your management. You’re in a good situation right now, but that can change. I was in a similar situation several years back. My boss liked me and had a lot of connections. He would make sure I was in the loop on everything, make sure I had a seat at the table when decisions were being made, and seek out my opinion on what direction we should go, and told me point blank I could speak for him or any other manager and he’d back it up if needed.
We have a whole new management structure now and they are very top down, have big egos, and aren’t willing to even entertain feedback. Vocal low level managers or engineers have been getting pushed out of the company left and right, so all the autonomy and the voice I had are pretty much gone. Even things that I thought were engineering decisions have been largely removed. I will need X to build what I’m building, so I make it and it worked. Then, months later, I’m told there is a different plan for X, I did it wrong, and I’m told to remove my solution (fully automated and hands off) in favor of a corporate process and manual work by other team, which is often missed, which makes my service less reliable.
I’m glad I’m not a manager who needs to fight with these people, as I’d probably be out of a job by now so they can replace me with one of their friends. That being said, I’ve found the influence of a senior level engineer to be highly variable, even within the same company/team, on a longer timeline.