Yeah I've stopped summoning help for bosses. It trivializes everything.
I went through belfry sol yesterday. Got invaded like 8 times, lol. Maybe I don't understand it well enough, but the PVP in this game is kinda dumb. It's not really an inconvenience, but the invader seems to have too many advantages including multiple invaders attacking me, not being aggro'd by mobs etc. I've noticed some invaders don't use estus flasks, but some do. Not sure if they can't or choose not to because it's cheap.
I'd love to finish the game and go PKK like I usually do in games that support it, but doing it via the blue sentinels seems like a hassle.