I understand what you're trying to say but I don't agree with the rod action part of it. If it does make a difference it's so minute that it wouldn't be perceivable by us. 2 graphite rods by the same maker, 1 XF and 1 MF with everything else being equal shouldn't have any perceivable difference in sensitivity.
If you're talking about slack line sensitivity the rod isn't bent or under load so the action has no bearing on anything. If you're talking about, let's say, dragging a jig, the line is tight and as we've agreed on, a rod under load with tight line will transmit vibration better. If you're fishing a properly weighted bait to the rod, there won't be much bend at all while fishing a bottom contact bait anyway. The action is only going to change where the rod is bent, not how much it bends, as that is power.
As for line, in my opinion, 2 things make fluoro more sensitive than mono, the density and hardness of the line and the fact that fluoro sinks. (Or is that 3 things?) The sinking line gets you closer to your bait with less bow in the line so that you're closer to a tight line even when it's slack.
I'm not even sure if that makes sense, it's been a long day. lol