Again, I'm not seeing Hydreigon as being entirely outclassed by any of the above dragons. Otherwise it would be "D" rank rather than "B-". Furthermore it rose because of its life orb set which means that it must have some merit over Kyurem-B (I won't discuss Hydreigon's pros over KuB as I did that on the first page). I've found leftovers KuB to be a little too weak and while sub helps prediction I found it missed out on some 2/1HKOs (most noteably a clean 1HKO on Azumarril which is why I'd pick KuB over Hydra in the first place most of the time).
Latios is much faster but does anyone use it as a true wallbreaker? It's actually fast and its access to defog is something Hydreigon will never have which is great. I've never found dragon/psychic a great STAB combo (it's fine just not great) and it has this annoying pursuit weakness. It has plenty of other upsides but its inability to beat Heatran without surf makes me leery of treating Latios as a wallbreaker. I don't think you can compare Latios to Hydreigon as they have very different rolls. As boltsandbombers said though tailwind Latios is awesome, underrated in any offensive team, and a great partner for Hydreigon :)
Again, Hydreigon's main competition as a wallbreaker is KuB and I think Hydreigon has enough unique attributes to justify its use over the ice dragon. As Jaroda alluded to last page, Dark Pulse has awesome neutral coverage and I find it to be a better main attack than anything KuB offers. This comparison does lead to interesting discussion though.
Jaroda, your set is interesting but have you ever wanted more power? Why not just kill what you switch into?
Edit: forgot about Latios' EQ which is for Heatran and pretty much nothing else