Perhaps we should take a step back and consider, in general, how a Protestant might make a case for his position. Take a comparison: it's been said that you don't need direct evidence for the theory of evolution because, if there is no God, then something like (naturalistic) evolution must be true. If atheism is true, then the origin of life had to have a naturalistic cause. By process of elimination, that's the default alternative.
By the same token, a Protestant can operate with the negative principle that unless there's good reason to believe that certain Catholic essentials or distinctives are true, then he lacks a sufficient basis for rational assent. A Protestant might add that not only is reliable evidence lacking for key Catholic tenets, but in at least some cases, there's positive evidence to the contrary.
Furthermore, Catholicism is a package deal. It isn't necessary to systematically disprove every Catholic essential or distinctive. If you disprove even one sine qua non of Catholicism, even one dogma, then that's sufficient to discredit Catholicism in toto. It has no give in that respect. To the degree that Catholicism is a package deal, it's inflexible, the way Newtonian physics was inflexible. Newtonian physics was such a tight package that it couldn't be modified–it could only be replaced.
Consider some elements of Roman Catholicism:
• Authoritative tradition
• Apostolic succession (in a technical, Catholic sense)
• Papal and conciliar infallibility (under specified conditions)
• Prayers to the dead
• The perpetual virginity (including in partu virginity), Immaculate Conception, and Assumption of Mary.
• Veneration of relics
• Priestly absolution
• Baptismal regeneration
• The intrinsic evil of artificial birth control.
• The intrinsic evil of lying
• The indissolubility of marriage
That's a representative sample, but not exhaustive.
Now, if Christianity is true, but one (or more) of these tenets is false, then that falsifies Catholicism. Then something like Protestantism must be true instead. Or, if there's insufficient reliable evidence for one (or more) of these tenants, then we are warranted in withholding assent to Catholicism. Or if, in some cases, there's reliable evidence to the contrary, then we ought to deny it.
(Right now I'm discussing the Catholic/Protestant debate. We could construct a parallel framework for an Orthodox/Protestant debate.)