I know people are aware of how powerful Dr Milan is. I've now tried a few decks where i deliberately didn't take him. I can honestly say, this man is so incredibly powerful, that not taking him, is a deliberate, and non-power-gamey choice. If you want to win, and you are using book, and you have access to this man, there is no reason not to take him. Other allies can do other things, but this man helps you win the game, and gives you more money for doing so to help you play more things. He just combines 2 things you need in one card. I played a Trish deck most recently, that was still focused on using book. And I felt his absence. The lack of the boost to a baseline 5, and the lack of drip feed of economy was so painful it made me question my life choices. This is in a context where I consider Magnifying Glass just Forbidden for being too good. On the math, Mag glass is better than Milan since you never spent the 3 or 4 resources for him, saved an action, and you still get the boost. Milan at least means you have to consider the slot.
This man is too damn powerful, and, yes, you can win without him. But the difference between having him and not is so apparent each time. This card is S tier. If you think the game is too easy, just play without the good Dr. No need to go to Hard or Insane difficulty. Just adjust the player cards and remove the S tier options, and feel the difficulty rise.