I have not played as many games as K, Kissblade, CP or theJeff but I think I have played enough to have a healthy respect for heavy bless nations. Quick expansion, not just against indies, but also against other players can often net enough provinces to put them in a very strong position as your nation goes in to the middle game. As more provinces (and capitals) mean more gold (so more mages) and more gems in the medium to long term.
Where I think K has more of a point is that such growth and aggression can lead to gang ups. But it's not a sure thing. While it's in everyone elses interest that the early leader is taken down it is not in most peoples interested that they do much of the actual fighting - except the vital task of grabing provinces after the early leader power has been broken
So such gang ups are fraught with difficulties. Plus there is seldom just one early leader or heavy blesser for everyone else to concentrate on. Nor is a successful early rusher easy to take down even in the mid game thanks to their large number of sacreds and the boost the extra lands, income and gems give them.
But while successfully using a dual bless only
might result in a gang up, casting Utterdark certainly will. You basically kill the chances of many (most) other nations. They are dead unless your global is dispelled. While there may be some trust issues they are dead if they don't cooperate against you. Thats just not the case with an early bless fuelled leader. He only might be ganged up on and often only half heartedly at that.
I think the risk of a heavy bless strategy is not that it succeeds and puts you in such a strong position that enough enemies gang up against you but that it simply fails. An early bless rush is not a sure thing even against a none bless nation. All none bless nations need to have some defence worked out vs bless rushers. And while it is usually in the long run fatal to be the victim of such a rush you can't always be defeated in time (or even at all) to make the cost of the rush pay for the heavy blesser. And of course having paid in design points for a heavy bless sometimes you may find yourself surrounded by other dual bless nations and so with no comparative early advantage.
I think the original poster suggested that a D9 bless was as useful early on as an F9. Despite marshelling some interesting arguments I and most of the responders don't think this is so in most cases. There may be some scenarios where they are equal. But for early expansion F9 is usually a lot better.
But you don't have to buy in to K's Utterdark strategy to accept that having D9 on your Pretender is more useful spell casting wise than having F9. There are exceptions, but if you were offered a D9 Hero or an F9 one most nations would rather have the former.
Nor is it especially controversial to say by the mid to late game the F9 bless - while not useless - is not that big a plus as it was. F9 is at it's most useful in the first couple of years and declines in importance as the game goes on. You need to make it pay early in most cases and it's certainly strong enough to do that if you have the right kind of sacreds. While the effects of a death bless are still useful even in the end game, possibly more so when spells can affect the whole battlefield. Sure it's better to kill enemy SCs, mages and armies than afflict them, but thats still a useful side effect.
You don't see that many D9 blesses. For anyone to spend the points on a 9 or 10 bless of any kind that final bonus has to be good. And the resitable disease/2 AN just isn't. The main boost of the bless is the extra afflictions and the end game high death caster. But you don't need D9 for those. There are very few nations or scenarios I can think of where I would rather have an imprisoned D9 over a sleeping D6 Pretender. Thats still a +200% affliction boost and gets your Pretender up and about much sooner. Quite frankly Death 4 still gives you an affliction bless and opens the door to the death Thugs, Tartarians and the late game death spells at a fraction of the cost and without all the summoning X to call Y to summon Z needed if you have little to no death on your national mages or pretender.