Your Holocaust example is exactly where the problem becomes more serious

Suppose:

A, B and C = studies about the Holocaust

and:

D, E, F, G, H, I, J = perspectives that deny or substantially challenge the established account.

Now suppose institutions overwhelmingly fund, publish and teach A–C while D–J are systematically excluded.

You are right:

You cannot conclude that A–C are false merely because D–J were excluded.

But you can conclude something potentially important about the completeness of the scholarly picture.

And if D–J contain relevant evidence or arguments that should have been considered, their exclusion could make the resulting literature:

incomplete;

one-sided;

potentially misleading.

Gaza example

Similarly, if research about a conflict systematically examines:

Israeli perspectives,

while almost entirely excluding:

Palestinian perspectives,

then the resulting literature may be epistemically incomplete, particularly for questions concerning Palestinian experiences, perceptions or claims.

But again:

“The Palestinian perspective was excluded”

does not itself establish:

“The Israeli account is false.”

It establishes a problem of evidentiary or perspectival incompleteness.

To establish that the dominant account is false, you need positive evidence against its claims.

That is a fundamental distinction.