You throw that term "the law" around alot. What law? Which Congress passed it? Where is it to be found in the United States Code?
Yes, the USC, specifically Rules of Courts, authorizes the Courts to make rules, but rules are not the law. I'd bet that there are "exception" rules too. ... In fact I found one.
These rules govern the procedure in all civil actions and proceedings in the United States district courts, except as stated in Rule 81. They should be construed and administered to secure the just, speedy, and inexpensive determination of every action and proceeding.
Denying plaintiffs all access to the only things that would meet the standards of evidence and allow them to prove their case, can hardly be called "just".
Now you're questioning the legitimacy of the Federal Rules of Evidence? Oh brother. Every time I think I can't be shocked, anymore than I already am, I'm shocked.
Try out US Code, Title 28, PRT 5, CHPTRS 111-123 - or thereabouts. Let me know what you come up with.
Here's the best part of your post...
...They should be construed and administered to secure the just, speedy, and inexpensive determination of every action and proceeding.
No where in Rule 81 does it say, "Hey, you can ignore all the aforementioned rules to get to that just, speedy and inexpensive determination, now does it?
Denying plaintiffs all access to the only things that would meet the standards of evidence and allow them to prove their case, can hardly be called "just".
The US justice system isn't - in any way - about the delivery of justice, it's about the application of US law - nothing more, nothing less.
As a law professor of mine once said, "If you want to pursue a search for truth, talk to your priest. If you want to understand the law, you've come to the right place."
Consider The Federal Rules of Evidence. It’s the law.