Noone is; this turn we're doing Water Walking remember?
But if you're attesting neither is sufficient, the GCS is the logical next step.
We already know Tree Walking. We're learning Water Walking.
If despite everything, those two aren't adequate? Then yes, we want Graceful Crane.
It's not like the slots we spend on chakra training are free; they come at the expense of other things.
We unlock chakra tiers by training chakra techniques, not just by practicing chakra control.
In-universe, there is no suggestion that you can get usable chakra without living people, who get chakra depleted.
Nature chakra is only available to a very small number of people, and even they can only handle so much.
Electricity =/=Lightning-nature chakra.
More generally? You are trying to science what is basically magic. That never works well.
The Narutoverse is not a rigorous simulation with hard rules whose consequences were thought out ahead of time; a lot of shit here is Rule of Cool.
Poking at it too hard ruins the illusion.
If only because that's the only place Tenten got an actual characterization. 
