Forscher.....I think we had much the same conversation about the evidence back in December...
some scholars think that Paul's letters came first, before the synoptic gospels.
"Some scholars" is a bit of an understatement; it is the consensus view...This is different than the issue of whether there is material in the gospels contemporaneous with Paul, which is usually admitted by most...
What Leo didn't point out, is that opinion is based mainly on the presence of Prophecies in those gospels which were fufilled so accurately, that those scholars just cannot accept the possibility that they were written before the fact.
Internal evidence such as allusions to the events of AD 66-70 is indeed a key part of the evidence supporting a post-AD 70 date for the synoptic gospels. Such evidence is standard for assessing the date of any ancient work (i.e. quite apart from a desire to deny the possibility of foreknowledge), cf. the role of allusions to the Roman destruction of the Temple in assessing the dates of Barnabas, 2 Baruch, 4 Ezra, etc. But such allusions, at the same time, are not confined to "prophecies" (as implied above) but show up in parables and narratives as well. Nor are allusions to the destruction of the Temple the only kind of internal evidence, and there external factors as well that weigh on dating...such as Luke's dependence on Josephus...or the form of logia attested in Paul and other early sources.
It is also why they dismiss those ancient sources which put the writting of those gospels earlier, such as the one mentioned by Leo, as "not reliable".
It is not out of a desire of "dismissing" Papias that scholars have a mixed evaluation of him, but rather his traditions have a questionable reliability when assessed with other evidence. His statements on the gospels are also very difficult to interpret, e.g. was his reference to the composition by "Matthew" to our canonical Matthew or something else? But in fact Papias does not "put the writing of those gospels earlier" than is usually accepted today, as you claim. Regarding Matthew, he does not say at all when this was written, and with respect to Mark, he is quite clear that it was written from the author's own later recollections of Peter's teaching...suggestive of a date later than Peter, i.e. after AD 64, which is pretty close to the usually accepted date for Mark. In any case, he does not clearly put the writing of these gospels earlier than the accepted dates. Also, I recall when we last had this discussion, I pointed out that the Griesbach theory of Matthean Priority (and Papias makes no mention that Matthew was supposedly written first) actually contradicts what Papias says about the authorship of Mark, which leaves no room for Markan dependence on Matthew. Papias instead better supports Markan Priority (i.e. canonical Matthew written after Mark) when the interdependence of the two gospels is taken into account.