Well, I won IVAN latest official version best ending without doing anything bad (that is, without exploiting anything which was obviously a bug; some people might think that changing the material of your limbs is an exploit, but it is obviously a consciously designed feature, maybe it could be helpful to balance it a bit, but the help given by artificial limbs is not out of proportion anyway; there might also have been some people who won without using even that, I am not sure).
It's hard to tell what level of difficulty the devs intended. I remember them saying that this (i.e. the best ending) should not happen. Well, if they really wanted that, they could use some cheap way to make the game unbeatable, like forcing the player to go through 100 levels of monsters which kill in one hit and are virtually impossible to avoid, or whatever. (If passing one such level happens with probability <1/2 no matter what strategy you are using, then such a game would be practically unwinnable without savescumming.) IVAN does not have anything like that.