と言(い)うものでもないThere is no guarantee that…, Not necessarily

というものではない is an expression in Japanese that indicates that 'there is no guarantee that (A)', or that it is 'not necessarily (A)'. As this structure is just a combination of と, the う-Verb 言(い)う 'to say', もの 'thing', and ではない 'isn't', the literal meaning can be thought of as being similar to 'it's not a thing that one can say is (A)'.

は may be replaced with も, with only a slight change in nuance. As with many grammar patterns, the version with も will be considered a bit more emphasized.

というものではない may follow any word in its standard form, but may occasionally be preceded by だ when used with nouns or な-Adjectives (despite not being required).

In most cases, this grammar pattern will indicate that while most of the time (A) might be something that is expected to be true, there are exceptions.

Fun-fact

Although not specifically limited to it, というものではない sentences are often preceded by phrase including であれば. These sentences merely emphasize the fact that 'even if it's (A), it doesn't necessarily mean that (B)'.