Snaking is usefull, but that's not the point. The point is that it's usefull in a very little meaningfull strategical way gameplay wise. It has little or I'd rather say nothing to do with strategical planning that make sense in a strategical gameplay way. To put it another way: It has no opportunity costs attached to it, it's just cheesy. Unestethical too by the way.
As you say in your post. The usefullness of snaking can be alot better represented by other game mechanisms. Mechanisms that makes sense and have opportunity costs (like using ressources/time to build a fortress) or building buildings to improve your border radius, or plan city placements accordingly.
As I've said the use of snaking cities could and probably should have been better achieved other ways, but as things stands I simply cannot agree that the strategic usefulness of closing off an area with a snaking city is none because that just isn't true.
If I start on a map and after scouting find I can close off a considerable area with the placement of two or three cities which I can build via snaking to cut of entry to the map area with then that has HUGE tactical benefit. It provides you a large expansion zone you can utilize, loot and progress to yourself while the enemy leaders expand and squabble among themselves. Especially if you turn the blocking cities into Fortresses and quickly build walls and fill them with defenders.
Outposts can't do the job as they simply dont have the defensibility of city nor can you place outpost directly next to each other in order to block a path. And although border expansion is all well and good absolutely NOTHING stops an emeny crossing your borders (or a monsters) any tiem they wish to. And as the AI stands even if you use diplomacy and tell them to get out of your territory the very next turn after moving out they move straight back in.
Sure you could spend turn after turn fighting off tresspassing units but then you have a war and your resources and gold is then being used to build and replace units, meanwhile the progressesion and expansion of your blocked off territory is standing still largely or slwoly being utilised.
for me I enjoy the long games I secure a large area, and keep the peace while I expand, improve, research and build and that allows me to take a substantial progression lead over opposing leaders who invariably turn on each other in the meantime and then at the end I sweep across the map and destroy them all one at a time.
The strategic benefit of this apporach largely THANKS to snaking cities is undeniable.