That'a a big problem. It's a huge deal and Congress can either approve the whole thing or reject the whole thing. That puts a lot of pressure on the single representative.
It should be voted on in small pieces. The same should have happened with the ACA. There are lots of parts that could be enacted on their own.
The trickiness (and the whole reason fast track is a thing) is that Japan agreeing on A likely depends on the US agreeing on B (which depends on Vietnam agreeing on C)
It's hard to do compromise if the compromise itself isn't voted in. And when you're talking about 12 Nations...
OTOH breaking down legislation into smaller chunks to pass is definitely a good idea that isn't applied often enough (see immigration). Though that too can be tricky. For example you can't have the universal healthcare mandate without the preexisting condition refusal ban ( I have cancer and can't get health insurance , and now I'm being taxed??)
It should be voted on in small pieces. The same should have happened with the ACA. There are lots of parts that could be enacted on their own.