#1) as Fr. Cekada demonstrates, the legal language for making it binding is the same as that of Quo Primum
No, the language for making it a LAW is the same. The language of the law itself is non-binding. Paul VI does not say that it must be used, does not specify who has to use it, nor does he give a penalty for not using it. Pope St Pius V covers all these bases, explicitly and clearly.
#2) even if it's not binding, its promulgation to the Universal Church, and the promotion of its use, suffices to ensure that it's protected by the Church's Disciplinary Infallibility
Your opinion, which is overruled by a plain reading of Quo Primum and Pope Benedict. Quo Primum is the valid law of the Church's discipline because it has limits, parameters and is clearly written. Paul VI's law is also valid but only in the sense that it exists;
it's a law which allows no action, nor does it require action, because its allowance is limited by Quo Primum (and the writers of the law knew this, which is why they resorted to passive and indirect implementation of the law, because they knew that the law allowed no direct implementation.)
All Paul VI's law does is create a new missal. That's it.Pope Benedict's "motu" is a legal docuмent which affirmed that Quo Primum supercedes Paul's law and, most importantly, that Paul VI's law did not TRY TO overrule Quo Primum.
As with many things which the modernists do, they APPEARED to change the law, and IMPLIED that they did, but in reading of the law we find they changed nothing. Pope Benedict confirmed this.
Quo Primum did NOT forbid all other rites either; it left intact the Immemorial Rites, such as the Ambrosian, etc.
Quo Primum was VERY clear that it allowed a few specific exceptions (those rites which were 200 years in existence at the time). The number of rites excepted were quite few. All other rites not 200 years old were CLEARLY forbidden. The law is so clear on this point.
But that did not mean that any priest was permitted to suddenly start using the Ambrosian Rite. If applying your line of reasoning, one could argue that the Tridentine Rite was harmful to faith but that this did not compromise disciplinary infallibility because it left the Ambrosian Rite intact.
You haven't read this in a while, have you? It's very clear. If you go re-read Quo Primum, you will see that only those clergy who ALREADY HAD permission to use the rites which were excepted, were allowed to continue in them. A Dominican had no permission to use the Ambrosian rite, because he was of the Dominican rite. This did not change either before or after Quo Primum. The Dominicans were allowed to continue to use the domincan rite (if they wanted to, they could also choose to accept Pius V's rite. It was either-or).
The differences between Quo Primum and Paul VI's law are stark. Paul VI did not command, authorize or penalize anyone for saying, refusing, or ignoring his law. St Pius V did so and quite clearly, using the penalties of excommunication and disobedience to enforce his commands.