I believe Weapon Arsenal is fine as is, and would be overpowered adding anything to it as some have suggested. I think substituting a Combat Rover instead of a Soldier would be an understandable change. (Good idea, whoever suggested that.)
In the early game, you expect planetary pioneers to not be able to field advanced weaponry without infrastructure in place; simply recycling the hull into helmets won't cut it. So having a Soldier unit at the start makes sense.
My point is that having a unit with reasonable defense that, if used properly by not merely fortifying it at home, will reap nice rewards in energy, science, and culture depending on the resource pods they recover, and help scout out future base sites and future archaeological sites and sites to avoid (canyons and alien nests) will make explorations, expansion, and expeditions all the more efficient.
The moment you build a second colony, the quest completion gives you an instant second Soldier. Without actively devoting production to any military units at all, you still end up with two free military units, to be used to keep troublesome pests off your borders and contribute to the greater good by +0.5 positive health if you have the right Tier I military virtue.
Certainly, once you run out of resource pods on your landmass they have less utility as explorers, but they could still be used to guard artifact sites from rival explorers and so on and so forth.
I'm not suggesting that a Soldier has more usefulness than a free Worker or Pioneering, but I am suggesting it is just as useful.