I always thought LGDs were somewhat mastiff like due to sharing a common ancestor with the mastiff, but I'm really starting to rethink this.
And to circle it back to the LGD thing, we ought to make a distinction between mastiff and mastiff, as in pre-Roman and post-Roman, as well as post-British which would cover the modern side of things. It was Xerxes who brought mastiffs to Greece and as such, those mastiffs existed long before we had our own variety in the west. So in that sense, eastern LGDs certainly do represent a distilled old mastiff heritage, some more than others, but the effect of the "pre-mastiff" mastiff on the mountain LGD nucleus had surely been fundamentally profound. Now, because the "LGD" label covers a stupidly broad range of "breeds", it is assumed that they're equal in terms of genetics, which is silly. Western-European LGDs had zero pre-Roman mastiff blood, and in many cases it wasn't until the post-British mastiff blood was introduced that there was any "mastiff" involved at all. So LGDs are and aren't related to mastiffs. Of all kinds and time periods. Your understanding of the Mastiff's role on the modern "LGD breeds" is clearly sufficient enough to help you see through the romance.
Whereas some old mastiffs were assimilated into sheepdogs, others went into hunting types. That's where they split off enough that by the time they're ready to "come out", the respective mastiffoids will differ from one another depending on "host" family. So while the hunting/baiting side of things is the nucleus of the modern mastiff as inherited from Rome, so is the guarding/shepherding side its equal in preserving the mastiff as inherited from Greece/Persia.
And on the subject of Rome, something to keep in mind is the matter of what followed its collapse. What trends took over and what social repercussions followed? Anthropocentric view of the world brought on by new trends shifted the focus from actively participating in the refinement of usable Nature's creatures to making most animal breeders, especially dogmen, all but disappear for centuries, leaving food-animals as the only worthwhile endeavor. It's difficult to wrap one's mind around just how berserk that cultural shift was and how it disrupted our evolution. Them were some hard times. And they [u]lasted[/u]. Anyone who didn't want to fit in had the choice of becoming an outlaw, a herdsman or a monk. And it is those 3 groups of people which had preserved any and all continuity with the great breeds from before. All over the world, these 3 groups have done the same thing. Not only were they breeding dogs of known lineage, they oftentimes sat on treasures of historical writings and occult peds. Just like the eastern Euros hid their mastiffs in their LGDs centuries earlier, so did the heathen western herdsmen. They weren't hiding the same mastiff lineage, but they were doing the same thing. As circumstances allowed, they'd allow specialization for butcher's dogs and various stock-controllers, exposing "relatives" to one another and so on, until another trend, like let's say - the railroad, completely derails the comeback and leaves a bunch of "breeds" in its wake. And such.
P.S. Obviously, hunting lines of hound dogs kept by the aristocracy may have distant origins, but they ain't the mastiffs we're talkin'bout, so my apologies to the fans of the noble cur.