the 3rd exp is revealed

[Draxynnic]

Reapers certainly have some generally useful technologies that don't seem to have been used by the union much in the future besides the specific anti-esteq abilities, like the liquidator's neurotoxins, the culler's PsiTech, and the camouflage used by all of them. But it's more a question of role then technical advancement-the vanguard's robots are across the board relegated to support roles. As per their own fluff, this is a political decision. They could replace their infantry and combat vehicles with fully automated units, but don't, because having a human military as a glorified jobs program to get the unwashed masses off the streets and out of the core worlds is more important that whatever bit of utility the automated military would provide. After all, some refitted civilian robots, the autumn, can compete with actual military hardware well enough to be a major force. If the autonom were designed as a military force, they could be even more powerful.

Sure, there are political consideration involved... but I don't think there are necessarily significant military compromises being made - is a robotic soldier really better than an organic one in armour? Is a robotic war machine really better than a piloted one? Possibly a little, but not enough to outweigh the PR benefits of the soldiers being "like us". Keeping a human in the loop means that CORE isn't in direct control of every decision, there's at least some additional resistance to hacking over a robot, and people who aren't fighters might trust them more than they would a faceless robot.

And when it comes to colonisation, there are other practical benefits to the soldiers being sent to do the colonising being men and women who can settle and start the next generation.

Ultimately, though, even if you might be inclined to pull out logical arguments for robots being better soldiers than people, the overall theme of several factions in Planetfall seems to indicate that the elite of the Star Union didn't think so. Paragon soldiers are cybernetic rather than robotic. The Syndicate also rely on indentured soldiers rather than robots - maybe that is genuinely cheaper in the economic environment they're in, but never the less, that's what they use. The Assembly started out as a super-soldier project... but if robots are genuinely better, why not start there? It's pretty clear that the decision by the Star Union to rely more on human soldiers than robots goes far deeper than cost-cutting on the Vanguard specifically. In fact, if anything, the Vanguard seem to make more use of purely robotic units than Paragon or Syndicate forces.

What it comes down to is that the Vanguard seems to lack some of the advanced technology of the Paragon and Syndicate forces, such as Arc weaponry, Psi-Tec, shielding technology, and antigrav technology. However, there are a number of possible explanations for that beyond "the Vanguard is being deliberately underequipped". One of which is that Vanguard equipment has been chosen according to what is practical to keep running on an isolated planet. Another is that private forces of high-caste factions can afford more than standard issue equipment - which would be pointing towards Paragon stuff being just plain better, but budgetary constraints is not the same as a frontline military force being deliberately given substandard equipment. And in the case of the Syndicate, of course, it needs to be kept in mind that some of their stuff may have been developed after the Cataclysm.

Wildlife is a bit of hyperbole, obviously the vanguard don't need tanks and artillery pieces if that was all they were needed to fight against. But even the subjugation of the Kir'ko hasn't been presented as very one sided in the favour of the vanguard, and the kir'ko were missing a pretty significant portion of their planetfall era tech tree by their fluff. Defeating a very under equipped enemy doesn't mean the vanguard are the strongest force the star union could make them.

Not that one-sided, actually. There are references that indicate that the Kir'ko genuinely scared the Star Union, and that it was actually a pretty bitter fight, but one world against a large empire was only likely to go one way in the long run.

However, whether it was a pushover or not is irrelevant, the main point is that as a result the Star Union was certainly aware of the possibility that the Vanguard might run into organised opposition in the future. The first time around it was the Kir'ko, and they won that. Next time around it could have been a race capable of overwhelming the Vanguard, hacking their navigational systems, and launching a wide-scale assault across the Star Union with little if any warning. Or, less catastrophically, it could just be wildlife scary enough to wipe out an underequipped landing force.