My whole post is about the possible lack of hammer investment in the civilian fleet and how this could result in the availability of amphibious invasions without any strategic planning. Essentially, if you would notice that the future enemy had no military ships close to your coastline, then you could invade with your units without any thought of such an invasion in previous turns. You could invade on a whim.
I don't see what relation this holds to the section of your post which I quoted above.
We know very little about the mechanics of naval invasion. I just worry a little that the designers removed a major part of the planning of these tough invasions, that they are too cheap now. It could be that the AI always quickly builds some military ships. But I doubt that these will be present during every single turn on every single coastal tile to block any and all transports which might arrive from any direction. If sailing into enemy lands (and thus declaring war) plus disembarkation can be done in a single turn (nobody claimed this to be untrue and it has been true in every previous version of civ), then the only way for military ships to stop transports is by sinking them before the declaration of war of the invader.
There are certainly ways to design civ5 so that military naval ships can easily protect a long coastline, but such designs were never chosen in previous versions of civilization. So I wonder what your
guaranteed investment in military shipping is going to accomplish.
So, even though you give guarantees

, I remain worried that military invasions in civ5 might require less investment and less planning and might often be performed on a whim.
I sincerely hope that there is still a significant planning cost involved in amphibious invasions. And I don't mean micromanagement, but a relative high cost in time and hammers to make such an invasion into a success.