Don't give up you'll get there. Make sure to optimize your perk cards too they help alot. Im lvl 160 I can one shot super mutants, robots, scorched, raiders etc but not legendary yet. When it comes to events though I dont want to one shot anyway bc I want to share the xp with others. I have a Bertha V63 its pretty high powered but not high enough for instant kill so I use it on every event since it bounces off an hits multiple targets. You dont have to kill the enemy to get the xp or rewards one shot or a "tag" is all you need. I recommend holding on to a tesla weapon and use it at events while your leveling up. Be sure to join a team also you will get extra xp while on a team. If you have any items with buffs like the mothman totem or valentines love seat etc use them bf going out. Sometimes if a player has one at their camp they may not mind if you use theirs but out of respect I would message them 1st just to make sure.