For the examples you put with juugo ( and by extansion the cursed mark), it's an external source who do the job.
I'll stay simple: Juugo get the natural energy, transforms it in chakra to use for others. Using ( and not gathering only) senjutsu chakra for non-initiated user, put them to death by petrification. It's stated by manga. Senjutsu is not an energy easily usable. The only one who screw the rule with a big asspull is Madara.
Sasuke can sense natural energy, true. His sharingan give him the ability to see it to a certain extant.
Can it be used to him ? Yep if the senjutsu user transform the senjutsu nature in simple chakra nature, otherwise it could "poison" the receiver.
Can he use it like a senin ? Logically, if he trains for it yes, but technically he can't for the reason under.
Can he become a sage ? No. Mainly for the reason many put: he doesn't have the chakra tank for it.
Sasuke have a stronger chakra, but he don't have enough quantities, so senjutsu is out of question.
It's like fulling a bottle of alchool: no matter how the liquor is strong, if you can't fill the bottle of the appropriate quantity, you can't sell it.
Though you tried to prove your point with manga points, and for that I put a good rating to this thread.
