Agreement
I actually agree with the Deathless ability. I don't think it's very powerful at all. He is right about the Diehard feat. That's a power you can get at first level. If the Deathless power were changed as you want it to be, Mellubb, you would have to be 14th level before you could get a less powerful version of a first level feat. Also, the saving through becomes VERY difficult for any REAL damage. It doesn't make the person a god. Even at -20 hp (which is ONLY 10 points of damage above normal death) you would have to make a 30 DC check. 10 points of damage is very small at that level.
Just my two cents.