The ash system is perfect for ER. I'll go even further to say that if they had included it in previous Dark Souls games it would have improved them.That's the thing with all these Souls games, they are so much harder single player than multi-coop. Every single boss going back to Demon's Souls is made so much easier if you just summon someone in to help. You just need someone to hold the boss's focus and go defensive, other people go in for hits, then rinse/repeat.
I'm not sure why they brought in the ash summons for this iteration, my feeling is because they want to make this game more appealing to the general gamin populace, and on that end they have succeeded. Probably a quick fix is that the boss should scale and become harder when you use an ash summon, just like it does when you summon another player(s) in.
I don't have a personal issue with the ash system, I think it let's people get over the most frustrating parts of the game without having to resort on other people. I personally try a boss with no ash, then if I hit a wall I'll use mimic tear. I tried summoning other people to help but it usually ends up worse than if I try myself with the mimic so I gave up on that a while ago.
My only comment is that the game should include a "hard mode" that removes them from the game and some other stuff. But at the very least it's an easy thing for a player to chose to drop. I'm doing that now and slowly working my way through the game and I'm already having more fun than just hiding behind the mimic tear.