Usually there is something in Applications causing these files to be recreated in my experience.
Crappy PDF apps, coupon programs, poor video players etc - however helpermcp relates to a crumby program called Mac Cleanup Pro. If that doesn't exist in your Applications folder, try searching in Finder across your whole system for it and consider removing any files relating. Then, removing the plists in LaunchAgents and Application Support should be permanent.
I'm finding Safari gets completely corrupted on pre-Catalina MacOS by SafeFinder, I cannot recover it from redirecting to affiliate driven yahoo search. I suspect there is a way of altering the plist files in /system/, be ace if anyone can help in that regard.