Your whole extended statement fell apart with the title.
"NSL = for things that DO NOT require a warrant"
Actually, warrants are the mechanism by which a free society achieves balance between personal and collective rights. Absent that...
Nope. Not everything government does requires a warrant. That is an undeniable fact. The case law which says metadata, for example, affirmatively does not require a warrant, has no expectation of privacy, and is not covered by the Fourth Amendment, is over 35 years old.
It got even weaker when you stated that "NSLs DO have massive amounts of LEGAL oversight..." States facts not in evidence. What, exactly, are these "massive" oversight mechanisms?
"Hey, can you help us out..." is laughable because you characterize this as a friendly understanding between actors who know each other. In fact an NSL is 100% coercive, cannot be challenged, and it's secrecy is the ultimate weapon. An NSL compels the recipient to do as demanded and never tell anyone else. The NSL itself could be illegal but the recipient cannot even inform a lawyer, as that would violate the secrecy provisions. Oh, but do tell us about the "massive" oversight.
But NSLs -- which are nothing more than a letter -- are not illegal. That's the point. In fact, the only thing found unconstitutional about NSLs were the extent and length of the gag orders accompanying them.
By your logic, any law enforcement or government entity should NEVER be able to approach a business about anything and ask for help. It should ALWAYS require a court order, no matter the information requested. That's how you might think it should work, but that is not compatible with reality.
When you state "...if a NSL is used, the person is almost certainly a foreign intelligence target under active investigation..." you put the cart before the horse. Your language is that of conclusions concerning a criminal, as found by a court of law. Except this comes before a court of law has had any chance to hear a case. This is lazy argumentation to support a flawed process.
No, you are putting the cart before the horse by implying that a warrant is required for information or persons who fundamentally DO NOT require a warrant. What you are essentially saying is that a warrant-like approval process needs to happen for any sort of action or information request government takes or makes, ever, to ensure that the government isn't "lying" about it not needing a warrant...which defeats the whole purpose, and timeliness, of not needing a warrant.
Finally, you mention FISA. This joke of a process has a 97% warrant approval rate. Standard court warrants have about a 60% approval rate. Literally nothing else needs be said about how weak the FISA process is; statistically, this approval rate cannot be explained or justified. Except, by repeating what the FISA court really is: A one-sided process meant to produce a Yes answer, with no right of reply or rebuttal. Retroactive FISA warrants are further evidence of the corrupt/flawed/lazy thinking that produced FISA in the first place.
This comment truly shows your ignorance, because you have no idea how FISA works. At all. The IC does not approach FISA with requests that will probably get denied, because it is a massive waste of time and resources for the literal armies of lawyers who submit FISA requests -- for FOREIGN intelligence collection -- on behalf of IC agencies. Law enforcement agencies, however, do this all the time because they have no other choice but to try. So your assumption that just because the approval rate is high is because it's a "rubber stamp" and really doesn't care about what it's approving is false.
Of course, you have already made up your mind and use a lot of specious and absolutely false logic to arrive at your conclusions, so this conversation is moot.