It's not a bug, it's a feature.
Some "questionable" tactics were pointed out to Thomas, he agreed that they were bugs rather than intended features, and he patched them accordingly.
Now, is the game harder because of it? Well, if you regularly used some of the patched things, then most likely yes. Otherwise not. Is the game unwinnable because of this? Some YAVPs say that it isn't. Even with those squishy MEs.
The thing that makes ADoM different from other roguelikes is potentially infinite loot/gameplay - after all ID is infinite, and creature generation is infinite too. So potentially you can have all the items you want/need given that you spend enough time on obtaining them.
Personally I am of an opinion that there's nothing wrong with extra loot/stats/etc. But it should not be matter of time/grinding, but rather of risk/reward. What I mean is that getting extra loot is fine, if you have a chance to die horribly for it. The better the loot, the worse the opposition. That's how ADoM should be :).
Now the question would be, how to setup such a thing. Because, how it is now, one could endlessly and with little to no risk grind some level in the ID over and over again. Which isn't much fun, really.