Underrail is ~80% combat while Arcanum is ~30%. One is clearly more combatfaggy.
During my last Underrail playthrough I fought less than in any of my Arcanum playthroughs.
I'd agree about the Expedition with it's native attacks/ pirate raids and old ruins filled with things wanting to kill you, but the base game is filled with opportunities to avoid combat, both during the quests and exploring.
The only quests where you are really forced to fight are the Arena, the Beast in Forge, killing Balor (can be assasinated), final Black Eel quest, Gorsky's final quest, second and third main Protectorate/ Free Drones quests, Core City warehouse shootout and the end of Deep Caverns.
Every other fight can be avoided with at least one of these:
stealth/ stealing, persuasion/ intimidation, hacking/ lockpicking, money or disguise/ security pass.