> I recommend using the backlog as a diplomatic tool and a polite way of letting things get lost.
I hate this approach. I totally get it, to be clear. I've done it. But I hate it. It's a sign of a really bad culture if you have to placate people in this way.
If your senior leadership is clearly communicating priorities, you should be able to say, "Look, this is an interesting idea, but as you know this quarter we're very focused on X, and this just doesn't align with that. The best route to get this done is to give your feedback in the next planning process and see if you can push Y to be a priority, then we can definitely talk about getting this on the roadmap."
A huge part of the job of a PM is to say no. If people aren't able to take a no on feature requests, there's a problem somewhere. Maybe it's with the way you're delivering it, maybe it's with the overall culture or maybe it's with the person making the request. Whatever the issue is, though, it's better to deal with it and create an environment where people understand that sometimes their requests will get declined for valid reasons.