So try doing a SL1 run if you think it's too easy. If you think phantoms make the game too easy, don't use them. Even with phantoms, a no death run is still a significant challenge. If you disagree, record yourself doing a no death run, obtaining the item you get at the end of it, and then you can make that claim with the proof to back it up
I can understand someone like yourself who has played the games so many times that they feel they're too easy now... but that's just because you've developed skill. Even if they jacked up boss health, you would still learn their patterns and dodge all their attacks anyway. Short of making attack patterns ridiculous so only the top .01% can beat them, they won't be able to satisfy the level of difficulty you desire.