Not really. Most of Gnostic Christian texts are later additions and majority of scholars have very good reason to believe that John's book is also not part of the earliest tradition contained in the synoptics.
When it comes to Mahayana Prajnaparamita sutras, the followers themselves record that these were supposedly "
secret" teachings kept aside by Buddha not known to anyone until they were discovered from beneath the sea at around 1st century BCE.
For example, the heart sutra was composed in China in around 200 CE.
Heart Sutra - Encyclopedia of Buddhism
However, based on textual patterns in the Sanskrit and Chinese versions of the
Heart Sūtra and the
Mahaprajnaparamita Sutra, scholar Jan Nattier has suggested that the earliest (shortest) version of the Heart Sūtra was probably first composed in China in the Chinese language from a mixture of Indian-derived material and new composition, and that this assemblage was later translated into Sanskrit (or back-translated, in the case of most of the sūtra). She argues that the majority of the text was redacted from the
Larger Sutra on the Perfection of Wisdom, which had originated with a Sanskrit Indian original, but that the "framing" passages (the introduction and concluding passages) were new compositions in Chinese by a Chinese author, and that the text was intended as a dharani rather than a sūtra.
[7][18][19] The Chinese version of the core (i.e. the short version) of the Heart Sūtra matches a passage from the
Large Sutra almost exactly, character by character; but the corresponding Sanskrit texts, while agreeing in meaning, differ in virtually every word.
[20] Furthermore, Nattier argues that there is no evidence (such as a commentary would be) of a Sanskrit version before the 8th century CE,
[21] and she dates the first evidence (in the form of commentaries by Xuanzang's disciples
Kuiji and
Wonch'uk, and
Dunhuang manuscripts) of Chinese versions to the 7th century CE.
So, yes, almost all Mahayana sutras were composed centuries after Buddha himself.