It's possible that they had some plans for how to end the show, but when they got the green-light for season 7 they postponed them and had nothing to fill the gap, so we get a lot of poorly thought-out filler material. Combined with the fact that the opening arc drained a lot of their creative juices early in the season, and season 6 ends with a major slump.
That a lot of the ideas we eventually see in season 7 were already being kicked around in the prior season is attested by Statistical Probabilities
especially, but, I think also, The Reckoning
So... I think that makes sense. Getting the Romulans involved was the one trigger that was pulled, brilliantly, in season 6.
The Sound of Her Voice
works ok, imo, as a kind of "calm before the storm" sort of episode, a little like In the Cards
prior to Call to Arms
, though that one is more comic, while this one has a contemplative/ominous vibe.
And the season finale does deliver, though perhaps not in spectacular fashion. My only real issue with it is that there has been too much of a lull already, in this season. So, we didn't really need a contemplative/quiet episode at this point.