It seems a rather oddly conceived collection. Having seen who's included from the tetrarchic/Constantinian era, and who's not, I'm left scratching my head as to what definition of a "Tyrant" was used as a criteria. We have Constantine I included, represented by a decidedly random group of 3 solidi, but none of his sons (either as caesars or augusti), nor his eastern co-emperors Galerius, Maximinus II and Licinius. The grouping by rivers is odd too. I suppose this was meant to be cute or something, but it seems pretty random. The roman emperors are all considered "Tyrants of the Tiber" regardless of whether they were western or eastern based. I agree the whole "most valuable collection" marketing angle is pretty tacky. It's hard to guess if this is what O'Dowd regards as the most significant aspect of his collection, or if this is just targeting a particular tacky audience who want to go see a billionaire's collection. The website does nothing to alter the impression of tackiness and non-numismatic focus, with emperors sorted only by name rather than date, yet his "book store" (where he's flogging $10 brochures of each part of the collection) offers 9 different sorting options for his 7 "products". It was cool to see his US type set (or part set - whatever it is) all on one page, especially as I'm not familiar with it having grown up in the UK learning about British coins instead. Well, each to their own, but with unlimited resources I'd have thought a complete collection of something would be more impressive than "most valuable coins of random dudes living on rivers, of whom you might want to buy a $10 brochure".
That seems rather dismissive. Regardless of whether or not you find the conception and organization to your taste, belittling the collection in that way honestly seems kind of petty to me. Personally, I'm far too impressed and lost in the amazing quality and beauty of the coins themselves to complain about the presentation and marketing. At least Mr O' Dowd has published his incredible collection online for everyone to see. I don't see many major collectors doing that.