I think this is perhaps too reductive. Part of getting to Magnitude 4 is that we get an additional Focus action, but surely that is not the ONLY part. I imagine that there are other factors at play that are going to have more impact on things. Recall the original definition of Magnitude:
So I don't know if we can just look at the raw calculation for successes from focus actions and make decisions purely based off of that; it seems like it would be neglecting a bunch of other important (albeit more difficult to evaluate) things.
I broadly agree.
Though to extend on this, collector trees right now mean that focus actions are more efficient spent growing ANYTHING - collector trees, other special trees, the worm, the forest as a whole - as opposed to focusing elsewhere. It is still efficient to use our Focus action for a different growth task; it is just that Collector trees are also our most immediate and scalable investment vehicle, so the opportunity cost of not working on them is that we forfeit the future resources they would have otherwise produced. Though to be fair, we can't spend resources if we are dead, so so for a sufficiently urgent crisis that cost might be worth it.