Can somebody explain to me the difference beetween these two grammatical forms? They both seem to have the same meaning of "it doesn't mean that" ,and also they are both used at the end of the sentence. Perhaps, the difference is that というものではない, must be preceded by a verb or adjectives in ば form?
I think this question is essentially about the difference between 訳だ and ものだ.
Only 訳 can describe a reason-conclusion relationship typically described with words like "because", "therefore", etc. もの focuses on a cold fact, a customary obligation, or "common sense".
For example, when you give a general fact or advice, the following sentences are roughly the same:
It's not that an expensive gift is always good.
However, you can only use 訳ではない in the following situation:
I did say I like baseball, but that is not to say I want to be a baseball player.
- [??] 野球が好きとは言ったけど、野球選手になりたいというものではない。 (highly unnatural)
In this case, you are trying to deny a false reason-conclusion relationship, and the latter half of the sentence has nothing to do with common sense or customs, so 訳 is the natural choice.