Why don't you cite Vatican I where you claim that it contradicts their statement?  If you're making the assertion, it's up to you to cite the relevant texts instead of having someone read your mind about what you're thinking, read all of Vatican I, and then try to guess what you have in mind.

Apart from that, the argument of "ecclesiavacantism" has been debated here a lot before, without any clear winner.  Threads have gone on for many pages on the subject, and it needn't be rehashed here again.

I hold that they're factually incorrect, and that there are some Sees in which the occupant formally exercises episcopal authority, based on the principles of the sedeprivationism.  They would need to articulate their reasons, but I would disagree with the proposition that everyone who remains in the Conciliar Church is ipso facto a non-Catholic and outside the Church.  On top of that, sedeprivationists would hold that they can have material designation to authority thorugh a "material" pope, while sedevacantists have cited texts asserting that jurisdicition can pass though even Antipopes via "color of title".

In any case, it's also by no means proven that the Church could not at any point have no bishops with formal/ordinary jurisdiction.  If you don't believe that there are other mechanisms to pass jurisdicition even during an interregnum, then during EVERY interregnum, no bishop has jurisdicition, since there's no pope.

It's not a straightforward / easy syllogism that R&R often claim that it is, just like they throw out there the "perpetual succession" nonsense that they widely misinterpret.

I make the following analogy.  Human beings essentially have both a body and a soul.  But when they die, before they are reunited with their risen bodies, they do not cease to be human, nor does their essence change where they no longer require a visible body in order to be human.  It's merely an accident that for a time they are lacking their bodies.  One could make the case that, similarly, the Church essentially requires both a pope and a visible episcopate in order to be the Church, but this would not prevent it from accidentally lacking either a pope (during an interregnum) nor a visible episcopate.  In a sense, there is no visible episcopate with jurisdiciton without a visible pope with jurisdiction ... and so this would actually be the case every time a pope dies or resigns and before a new one has been elected and has accepted.

Apart from that, the argument of "ecclesiavacantism" has been debated here a lot before, without any clear winner.  Threads have gone on for many pages on the subject, and it needn't be rehashed here again.

You wouldn't have a purpose in life if there weren't endless stalemate debate threads