Wait, you say that the game relies on RNG and random bullshit, then defend The Lost as a "challenge"?

The game wasn't designed with a 1HP Wonderboy in mind. Sure, there are achievements for beating floors without taking damage, but those are achievements; little extras that challenge you to go above and beyond with your gameplay skills. But there are floors and rooms that hold enemies who can very quickly damage you (spiders, headless IPECAC enemies, fricken laser beams being amongst those), and taking them on has a high risk of damage to your character. With a character who cannot take any damage whatsoever before falling over, that's not a challenge, that's an exercise in frustration.

You say that it's possible to beat The Lost without the special go-to items. That special go-to items are referred to as such by the community at all should say something. People were using exploits (and still are using exploits) to make unlocking The Lost's items easier. The game can be beaten without the holy trinity of Dead Cat, Stop Watch and Holy Mantle, but the player needs to be at the very god-damn top of their game to stand a chance of doing this (see: Northernlion)

The Lost is an interesting character, certainly; but he doesn't belong in Rebirth. In a game built around players having a health-bar, a character whose sole trait revolves around not having a health-bar is bad design. Blue Baby was a more interesting character because his schtick involved a very limited health-pool. You could still utilize health items with him; you could still utilize on-hit items with him. The only things you couldn't utilize were red hearts, and Dark Bum/D20 can easily solve that quandry. Having to live solely through armour is more of a challenge because you need to think "Could I get some money from the blood bank and buy this item, or should I play it safe and try to tank the next few rooms?" or "Should I re-roll this health item into a potential damage item or range-boosting item?", not "Will this next room have laser enemies?" or "Will I be taking this boss drop at all?"