Seriously, every person I invade is accompanied by a bunch of phantoms brutally beating EVERY mob in the level. Have you forgotten what you're playing? It's Dark Souls, it's meant to be hard, it's meant to punish you for your mistakes or sloppy play. I've beaten all the bosses within ten attempts alone, without any summons on my first playthrough.
It's not like bosses in DS3 are hard anyway, plenty of DS bosses were way harder than the entire game is now. Play the game if you want to play it, if you want some cheesy *** MMORPG experience you should consider switching the game.