I don't deny it can be taken too far.
But, in itself, it isn't an error.
I would expect a clear condemnation from the pre-V2 Church of "this pernicious error that goes by the name 'Baptism of Desire'" or something like that.
Again, when the Church infallibly declares that the sacrament is a necessity for salvation, that is what She means - there are no exceptions.
If there were exceptions, the Church is perfectly capable of adding them to the declaration, but because she did not explicitly condemn it is no reason to say: "the sacraments are necessary except in certain circuмstances" - and whoever says this, per Trent, is anathema.
The fact that a BOD is not in any magisterial declarations does not mean the Holy Ghost simply forgot to add it.
The nature of a BOD is such that those who adhere to it are forced to compromise the doctrine that infallibly teaches of the necessity of the sacrament, as such, even when a BOD is some day infallibly, irrevocably and clearly condemned, BODers will still not accept it even though it be explicitly condemned as you suggest.
No different than the "Thrice defined dogma EENS" - why did the Church need to infallibly declare three times that there is no salvation outside the Church - yet people STILL refuse to accept that truth - and so the same can be expected when a BOD is infallibly and explicitly condemned.