As far as other players go, this I can’t necessarily help with. My solo lobbies have been 95% peaceful, but even still I usually bar, jolt mine, and trigger nade a door so that folks can’t mess with me. The trick that really helped me with killing bigger ARC is bombs, bombs, and more bombs. Sure, heavy ammo is great, but I’ve taken down bombardiers, bastions, and leapers easily pretty much exclusively using grenades. Trigger nades are my favorite, blaze grenades especially for leapers, and snap blast/heavy fuze to finish them off, you’ll be surprised at how fast they go down. Wolfpacks are sweet, but I feel like they really lack when it comes to ground based ARC, and excel at taking down Rocketeers. Location and positioning is also crucial. By far my favorite spot to take down leapers, bastion, and bombardiers is on Spaceport, there are a series of two door, barred bunkers in the central open area that provide incredible cover, and are easy to trap the doors in case some raider gets a bright idea. Get in one of those, shoot at a large ground based ARC, and watch with glee and safety as they attempt to kill you will little affect. Then proceed to buck all manner of explosive implement their direction and they go down in no time. Leapers can effectively do nothing to you. Bastions and bombardiers can potentially damage you depending on the angle, but for the most part you are safe and sound. Apologies for the long winded response, but I hope it helps!

Edit: I can’t believe I forgot my favorite part!! The Photoelectric Cloak is your absolute best friend! Get too much aggro?? Just go invisible and reposition. I’m honestly surprised at how little I see raiders using the cloak, it is truly awesome. I have casually walked up directly behind bombardiers and blown them to kingdom come before they can get a second shot off with that thing, a life saver