For TWs, there are two potential actions right now. One action is to begin looking into how we could mitigate the flaws inherent in TWs, and the other is learning how to handle making them in mass and training them to use their abilities.
These are two very different projects. While neither project is worthwhile if all TWs are a waste of time (not a claim that is supported by the in-quest fluff), the goals they set achieve very different ends.
The Biologis project is effectively guaranteed to have no impact in the coming fight against the Nids and company. While the action itself will complete before we are expecting them to arrive, the action is akin to the action we had for Tranth to investigate the Titan when we were rebuilding it. The reward is a path forward, but it is several steps short of implementable improvements. That said, it is a very good action if we plan to rely significantly on TWs going forward, as the sequence is likely to provide a significant improvement to all TWs going made after completion with no cost aside from that of the research.
The Munitorum action doesn't do anything for improving the makeup of Thunder Warriors, but is the gateway action to being able to field them wide-scale on Avernus. While it is a fairly long action producing a low number of TWs, it is not characteristic of how long or how many TWs an action will take and produce going forward. It is the equivalent of setting up the training and then making the first batch of Super Elite operatives—it's about figuring out the best way of doing things. This action will produce troops ready in time for the fight against the Nids, and will also likely allow us to mass create more batches in time for the fight should we feel it necessary.
I view the Munitorum action as being less critical to have finished by Nid-day than the training simulator one, but more important than the other Munitorum actions we have—in addition to providing a marginal benefit if finished sooner (by allowing us to train and deploy more TWs against the Nids, whereas the +skill only really matters that we get it done in time). I view the Mechanicus action as well worth it ordinarily, as TWs are likely to become an emergency response going forward as well as providing further options for things like psyker hunting, and are thus worth further investment in, but poorly timed given that we will not see any return on investment in the coming campaign combined with the fact that Biologis examination of the Nids is critical to deriving an accurate threat assessment of them and should thus be done as early as possible. While using a free action on that is also an option, given how much our normal action economy favors Explorator and Fabricator General options I'd rather reserve it for more typically in-demand options.