+Vigano has a duty to declare his prior sacraments as doubtful. It's part of the virtue of justice, to admit your prior path was wrong and that people were affected (even if you are not 100% guilty, for your prior path, since you were duped as well). I don't care if 0 people care and they all ignore him. It's his duty. His Guardian Angel will listen and note it all.
If +W and +Vigano (and every other Trad cleric who came from the novus ordo) would be more public with these conditional rites, and more vehement about exposing the new rites' doubtfulness, then Traditionalism would be stronger.
Please see my lengthy post on the matter. +Vigano has very deliberately taking it one step at a time, seeing his mission as bringing as many with him as possible out of the Conciliar Church into Tradition. He could "declare" the NO rites to be doubtful all he wants, but that debate has been out there for decades already and his taking a position isn't going to resolve the debate. On the other hand, in abruptly declaring the NO rites doubtful, he would lose large number of those who are currently still "following" him. What he's accomplished has been miraculous. Even Taylor Marshall admitted that 80%+ (my guess was closer to 90% in watching the livestream comments) supported +Vigano against Bergoglio, with large numbers agreeing that Bergoglio is an Antipope. So, the fact that +Vigano has been able to pull this off is a testament to his approach from the beginning. If he had come out on day one declaring that Roncalli/Montini-Bergoglio have all been Antipopes and that the NO rites are of doubtful validity, he would have completely lost Trad, Inc. and conservative Novus Ordites to the point that they would have simply written him off as another SV kook and stopped following his thinking. Instead, he's brought them (or most of them) step by step toward Tradition. That's a tremendous accomplishment that no Trad has been able to pull off. I liken him to St. Paul, who, despite his late conversion, was prepared by God to convert more souls than the other Apostles combined ... and part of his late conversion was key to his preparation for that mission by God.
How +Vigano works is that he'll take one step at a time, and with each step he also lays out the principles that will lead to the next step, many of which we've anticipated before he even made them. If someone is in darkness, shining a full spotlight in their face will not help them see, but will instead blind them, and cause them to turn away in pain. So the way to do it is by turning up the light little by little. You add a little light, allow some time for their eyes to adjust, then add a little more light, let the eyes adjust, etc. That's precisely what +Vigano is doing. He'll take a step, then go silent for awhile to allow it to be absorbed and to sink in, and in preparation for the next step, etc. He's using Bergoglio's own tactics against him.
Many/most Trads have already made up their minds about the status of the NO Rites, whereas the vast majority of Motarians have been assisting at Rites by these dubiously-ordained priests for decades and need to be brought along slowly, step by step. His making a public announcement at this time will not have any persuasive effect. I anticipate that his next move will be an explicit declaration that Roncalli/Montini - Ratzinger were also Antipopes. You noted that he's already implicitly done so, in keeping with his tactic of making one small step explicit, while laying the groundwork for the next step. Then he'll let that sink in among those followers from the Conciliar Church, after which I expect him to declare the NO Rites to be of doubtful validity. If he were to do that right now, he'd only be either 1) preaching to the choir (for those who already agree that they're doubtful) or 2) would risk losing many of the Motarians who would be inclined to reject that positoin.