It does have complete meaning, because if you're complaining about length, it's the EU that imposed that increased length, not the US.

That there's increased length at all is the problem. US is simply hurting themselves for allowing increased length.

Incorrect.

I don't see how it's not vague. Let's break your passage down, ignoring references to other sections:

each Party shall take into account

"each Party should consider..."

the need for proportionality between

"Any punishments imposed must be weighed between..."

the seriousness of the infringement of the intellectual property right

"However much money the complaining company thinks they lost..."

and the applicable remedies and penalties

"And whatever is/will be done to fix it..."

as well as the interests of third parties.

"As well as whatever value any related complaints add/subtract."

Let's put all that together, and bold vague statements.

"each Party should consider that any punishments imposed must be weighed between however much money the complaining company thinks they lost and whatever is/will be done to fix it, as well as whatever value any related complaints add/subtract to the issue itself."

The only thing this will do (and this is the only thing that will happen) is allow companies to come down however hard they want on anybody that angered them. Not just random filesharers, it'll be anyone that lost them profit. Which can mean anything from illegal torrenting to a bad review on Yelp. This will also allow companies that formed partnerships to increase damages to one particular person even if they had no reason to, if just one company out of the entire coalition got angry.

That wasn't your main criticism.

Yes it is/was.

However, that's also false: you just leave the treaty if you want to change laws that no longer abide by it.

Yes, let's just leave an entire trade agreement, thereby damaging import/exports until a new one can be made!