That bolded part is indeed a problem. You're not arguing about Convergence so much as you're arguing about some peoples' expectations for Convergence, as you interpret them. Forgive me if I'm more interested in substantive issues (such as what the actual consequences of the event are) rather than conducting a campaign to discredit part of the fanbase.
Ah. That would indeed be significant; but it's not necessary for Convergence to be a lynchpin in order for it to have significant consequences.
That said, the fact that the pre-Flashpoint Superman has spent nine years on the post-Flashpoint Earth-0, working in the background the whole time, strikes me as a significant consequence, and might even rise to the level of “lynchpin”. So even if you define "significant consequence" as "affects Earth-0 in some substantial way", I would argue that Superman: Lois and Clark has more in the way of significant consequences than Earth 2: Society has. (And frankly, I wouldn't use that definition precisely because it disqualifies Earth 2: Society from being consequential unless and until it interacts with Earth-0.)
We don't know that yet. Certainly, the solicit for Titans Hunt strongly implies that Lilith's visions only happened because of the Convergence. Could they have happened without it? Perhaps; perhaps not. But they didn't. And at this point, saying that Convergence has as little to do with Titans Hunt as Flashpoint had to do with Morrison's Action Comics run is premature.
I'm not sure he could have; it's premature to say. But, as with the Titans Hunt link to Convergence, it's largely a moot point: he didn't have other origins — not unless DC is doing something really weird. As for where DC is going with that, the solicit says that he'll be world-hoppingI don't know for certain where they're going with that, either; but it's too early to rule out pre-Flashpoint timelines.
Convergence arguably did more than just alter the origin for the Orrery of Worlds; it resulted in the pre-Crisis Infinite Earths surviving the Crisis, laying the groundwork for a post-Crisis infinite multiverse — not just 52 worlds; infinite.
To say that it was “utterly unnecessary” is a personal value judgment, not a fact. Likewise, you don't know the intent; you're assuming that it was conceived merely to fill a hole in the publishing schedule; but there are no facts to back that up.
Bottom line, though; I'm curious: what will it take for you to change your mind and agree that Convergence has lasting, significant consequences, and was not just a two-month filler?