KD, we were comparing a specific set of creatures - kobold to dragon. It would not be unusual for an adult red dragon to do 30 points of damage (I roll for damage, as do a lot of people, and that is quite well in the damage range for a single attack).
It might be possible, but it is still not likely. It is even not likely that most battles will be with anything nearly as powerful as an Adult Red Dragon. Fights of that power level might be 2% of all fights. The exception, not the rule.
And even then, the Bite of the Adult Red Dragon might often do 30 points (26 on average), but the Claw, Tail, and Wing attacks require criticals to even get near 30 points of damage (and even then, the DM would have to roll pretty darn high).
It would be unusual for an adult red dragon to do 30 points of damage with a single melee attack other than his bite.
He said it would be exactly equally effective against both, and I was disagreeing with him. And, you seem to agree with me on that point (as you started by saying "that is true").
The same of course holds true for other levels in my experience as well. Preventing 100% of damage from a kobold is a lot more effective than preventing 20% damage from something that hits for 15 points damage.
Yes, but where I am disagreeing with you is that the 100% drop is not a typical result.
Discussing the extremes is a bit disingenuous. One has to discuss the bell curve in the middle, not the most damaging and least damaging creatures to more accurately gauge the effects of the feat. What happens 95% of the time, not what happens 5% of the time.
Our fighter, who has the feat, barely noticed the benefit when fighting hill giants. I was talking from direct experience - one of our fighters has this feat, and as he's gotten to higher levels (we're only 6th level now) it's become less effective, with fewer creatures even doing that kind of damage. It's gotten so bad he's been asking me if he could switch the feat.
Odd. Maybe you have a player who forgets that he might not even have survived to 6th level without the feat.
A 6th level fighter typically has 52 or so hit points. A hill giant will on average take him out in 3 hits (at 18 average points per melee attack). The same fighter with the feat requires 4 hits to knock him unconscious.
I think this is something that is specific to your one player.
Compare this to the Tough feat. The same PC has 64 hit points and it still take 4 hits to take him out by the Hill Giants. The difference is that HAM does this all day long and if the fighter gets hit 20 times a day over a long day, it's the same as being healed with about 7 first level Cure Wounds spells. The Tough feat is like being healed with just over 1 first level Cure Wounds spell (based on how many extra hit points a day he gets).
Anyone with a little math skill can figure out that HAM is generally stronger defensively than Tough or most other defensive feats.
One final point on this. If the HAM feat saves the party 5 or 6 Cure Wounds in a day, that's 5 or 6 Cure Wounds that can be cast on other PCs. The purpose of the feat is not just to keep the fighter up, it's also to spend fewer healing resources on the fighter that can then be used for other PCs. If a player is complaining that HAM does not help enough, then he sounds like he's not looking at the big picture for the entire party.