RAM It is not about "cool stuff". It is about filling roles
Your proposal fills no role. But even with proposals that do fill roles like revencher, we can't fill all roles simultaneously. We are quite busy filling the role of cavalry and hunters are pretty good cavalry. Designing anything is saying -
Nah, we need no hunters after all. Next turn the pattern will repeat. All our designs will be useless that way. Designs are only useful when they are produced. We can't produce everything
And workers are obsolete for combat. We could benefit massively from a dedicated infantry unit with lower casualty rates
Probably. But there are no design that even tries to replace workers in a role of generic infantry.
We really need to design more efficient workers too,
We can design purely civilian units like lumberjecks or tunnelers or something but I don't think it is a great route to take. Nothing indicates that workers are inadequate
If we have basic flight then we can revise it for sea-combat, river crossings, siege infiltration, attacking flying castles...
We can't revise it for something... know why? Because spending turns designing useless stuff for some far future benefits will cause us losing war and being pushed back to Mentos.
If we have a basic stable of diverse options then we ought to be able to refine something into a counter fairly swiftly while furthering a desired biology.
If a have a number of diverse options of equal power, then it means wasted design power. Because our troops are inefficient.; Instead of having level 5 unit A, we'll have five level 1 Units A, B, C , D ,E. Way to lose the war
Vespa develops the very useful flight and grants pointy heads that work well for various "punching above your weight" tasks, along with being an effective cavalry-style unit that can focus down enemy special units such as wizards.
Ok, now I know your intention. You want a cavalry. I fail to see how Wespa is a cavalry (it is a very bad infantry in my books) but lets assume that it is a decent cavalry. Why the hell we need another cavalry when we already have one and it is quite decent and have good revision potential?
If you want flight for future. > Develop wings with a direct separate action. Not that we can afford more slow turns but it is far better way there.
Darters and bows, are, well, getting ranged attacks would be good, but I doubt they would work as intended without long-range sensory or prediction abilities.
Sure we need a flashy big effect to justify a design effect. No we don't. The whole thing with both darters and bows that they try to get more use from workers we produce anyway. Well darter may count as a new design and than it suffers all problems of new design. But bows (my preferred choice by far, but I think I should give up attempts to arm our bugs) are essentially free (well cost timber) way to get some ranged attack without redistributing production. Whatever new drone can't be free damage, it must be produced over something else.
Tactics, my current vote (BTW you ignored it in your analysis of proposals.) have a similar effect. They make drones we have and produce better without the need to change our production.
Also, from both tactics and bows I expect something somewhat useful effect even with 1,1,1 kind of rolls. No drone can be useful in case of bad luck.