But I'm suggesting more decisions...
At weapons are already nearly useless AI, removing the last bit they have really won't change much. Even then, I don't understand how that would be "brainless" and "dull".
Its brainless because there would be 0 downside to upgrades and just encourage death blobs even more so than we see today.
Think about it - you would have no reason not to spam PZGren Shrek Upgrades. Just keep them toggled off until you see a tank, mass toggle them on and then just 1 volley the tank and then go about your business.