It's not going to last twice as long, but it's worse than you've stated. We're about 2/3 done and at around 9M kills. So we'll get to about 13.5M kills at this rate, so not even going to be close to getting whatever the last boost is at all. I guess their spreading them out over the whole event was really making it so we wouldn't even get them all.
But really my bigger concern is like what sirlagalot is saying. In the past, you used to get better rates of all sorts of things, having event items like 75h sacrificial weapons and 50h rambling may, which are likely better than weapons I'll ever even get in any way. And with higher untekked rate in anguish and better boosts in past events it definitely feels like those that were here for the good times get a huge advantage for playing back then, even if they didn't play nearly as much as some players have now.
And yes, I understand the viewpoint of making it so that it's better to play now than later so that no one suggests holding out until later when there's more boosts. But at some point I feel that's taken too far and if everything just keeps getting weaker and weaker, it'll feel more and more like the best time to play was well in the past and it's just getting less and less productive to play now. If that's the case, at some point it might just not feel like playing at all. I hope I get someone good by the end of this event, as despite its nerfs, I feel it may still be better than anything we ever get again, so I'm likely stuck with never getting anything better than what I have at the end of this event again. And if that's the case, idk if I'll even bother with this any more after this event is over. But I guess I'll decide later.