I think you're shifting again from "could be doubtful" to "is doubtful". Below are two versions of what I think is the relevant part of the Ottaviani report. They say "could be valid" and "could also not be valid" based on intention. This reads to me as saying case-by-case and not that all new Roman Masses are doubtful.
Ok, good points, but you're confusing the prayers of the new mass vs the priest's intention. +Ottaviani said that
based on the prayers alone, there is positive doubt. This is because the new mass' consecration formula (as well as the deficiencies in the Offertory prayers) no longer make it clear the Church's/priest's intention. So, based on the prayers alone, the new mass is positively doubtful, 100% of the time.
One could argue that for 40+ years ALL of the masses which used the translation of "for all" instead of "for many" were 100% invalid. But I don't know enough about this; i've just heard people argue this. I don't think their argument is extreme, based on +Benedict's correction back to "for many". If it didn't matter (and I thought he said it did matter a lot) then there would be no reason for a correction.
The priest (if he's a priest) could supply the missing intention for the consecration. Then the consecration would be valid. But how would anyone know what his intention is? How many seminarians for the last 40 years have been taught that the mass is a "remembrance", a "memorial", a "supper", a "eucharistic celebration"? None of these ideals are sufficient for the validity of the mass, which is an actual sacrifice, the re-enactment of Calvary again.
The point is, one can NEVER know what the priest's intention is, unless you sit down with him and have an in depth interview which covers his entire theological mindset and his understanding of the mass. Even then, what if he has a doubt against the Faith one day at mass - a temptation to not believe? If he doubts that the consecration truly happens? Well, then the mass would be invalid because the prayers do not supply the intention, as they do with the True Mass.
The moral of the story is that the new mass is doubtful any way you slice it. And as I argued earlier, even if it was 100% valid, it is still illicit and immoral. So really, the debate over validity is irrelevant.
As you probably know, Paul VI sent the report to the CDF for comment, and Ottaviani's successor at the CDF did not give it a positive review. (Paul VI supposedly also made changes to the Mass before publication that addressed some points of the Ottaviani report.) In any event, after Paul VI gave a couple audiences explaining the new Roman Mass, and the new Mass was actually published, Ottaviani is reported to have written "no one can any longer be genuinely scandalized", though the text still raises "perplexities".
Every theological issue raised by +Ottaviani, +Bacci and the other theologians about the new mass is still there. Paul VI may have made some changes after their report, but his changes did not minimize the new theology, the protestantization of the mass, or the doubtful consecration.
+Ottaviani was not the only theologian who wrote the report. Even if he compromised his Faith by accepting the new mass, the objections raised in the report by the other theologians are still there. The new mass' problems did not go away.