For species with native environment far from inferno/radiated/barren or with bad industry, Exobots can be an asset. On the other hand, for species with inferno/radiated/barren native environment and good or better industry exobots are pretty useless (this is specially the case for Replicon).
@Voker57 may think something similar: https://github.com/MatGB/freeorion/pull/3
In that pull request, he suggested to nerf the exobots to be 75% research, 75% industry and 75% population and tolerate all environments as adequate.
Another concern of mine is regarding the strong effect of the flat bonuses to research (Nascent Artificial Intelligence) and industry (Adaptive Automation), that are close to no-brainer techs for every species (good research species must get it, and probably exobots, ASAP; good industry species can get first fusion and delay AA for longer while they build up enough colonies with NAI to accelerate research). Experienced players, correct me here if I'm wrong.
And finally, there is the issue regarding some very unlucky starting galaxy layouts that could make your game boring or frustrating, when your homeworld is surrounded by nothing but planets hostile or poor to your species as far as the eye can see. If you are are, say, Scylior, you then now you need Exobot ASAP (that you were going to get anyway, because of AA), if you are Replicon, you know you have to search further away or prioritise Xenological Genetics (although any of those mean you'll be way behind other empires no matter what you choose). Experienced players, again...
So I've got this idea, that may tackle (or alleviate) all three issues mentioned above, for your consideration:
- Change AA to give a flat industry bonus equal to HabitableSize (+1 for small, +5 for huge, +3 for asteroid belts... +3 for gas giants?) and be unlocked by Robotic Production and Algorithmic Elegance.
- Let the Exobot tech be unlocked by Robotic Production and Algorithmic Elegance, with the single effect of making outposts able to receive the NAI and AA flat bonuses (require Microgravity Industry to get in from asteroid belts, and orbital generation to get it from gas giants). So it would be useful only when at least one of NAI and AA have been researched.
- Remove the exobots as species, i.e. make them implicit to every colony and outpost of the empire once you get the tech (that would still talk about autonomous robots able to perform complex tasks in planets uninhabited by any species. Actually I like this alot, but haven't thought of it enough, and seems like a big change.
Expected consequences with this suggestion in place:
- Any empire can get some profit from every planet in its surroundings regardless of environment, so small empire strategies become more of an option in more starting galaxy layouts, and luck on the starting position becomes less determinant.
- The reduction on AA output (from +5 to an average +3), and the fact that empires would have a more similar progression on number of planets (not colonies), should reduce the early snowball effect of AA (I'm thinking of this particular case: currently, a research-focused empire with enough colonisable planets at start can get around turn 60 a production several times greater than that of a production-focused empire with few colonisable planets at start).
- Some more reasonable choices at start regarding research: for empires with no adequate/good planets around, Xenological Genetics doesn't become mandatory; AA is not the nature force it's been until now so can be delayed further in favour of other early game strategies (detection/stealth, better weapons/hulls, faster pop-based research boost, etc.)
Special point regarding Nerada (an unofficial playable species by @Jaumito that has the NO_OFFENSE_TROOPS trait). No Exobots as species would mean that NO_OFFENSE_TROOPS species would be unable to conquer enemy planets, never. That I don't like it.
- Add a new tech (within defense? growth?, construction? production? it is a hard one to categorise for me), unlocked by Exobots, to unlock a new special kind of robotic ground troop ship part that, regardless where it is built, it produces Exobot troop ships (possible glitch: if you produce in a Scylior colony an armed warship with a exobot troop pod part on it, would the pilot be Exobot or Scylior?).
A much less disruptive suggestion is that of Voker57's:
- Make exobots bad on research, industry, and population, and adequate on every environment.
- Change AA to give a flat industry bonus equal to HabitableSize (+1 for small, +5 for huge, +3 for asteroid belts... +3 for gas giants?).