The OP (if I understand him correctly) didn't want to worry about level at all.
I think you misunderstood me. I was just positing what would happen if you removed an, in my mind, extraneous bonus from everything. In other words, I was wondering how essential this half-level bonus actually was.
If, instead, he meant "simply impose a -1/2 level penalty on all PC and monster stats", then I agree that the net difference is the same.
That's basically what I was getting at.
It occurs to me that in addition to the "less difference" problem, subtracting the +1/2 level also emphasizes magic item choices much more than they are now, at least proportionally.
While this may be true from a purely aesthetic stand point, I don't think it's true from a mathematical one. That is, it might look like it makes magic items more important, but it doesn't.
That said, if your Nth level fighter doesn't have weapon, armor and neck-slot items with at least a +[(N/5)-1] bonus, then he's probably pretty gimped to begin with, with or without the half-level bonus obscuring things.
I don't think that's accurate, I think the problem lies in the peoples perception and there alone. Under currect rules, if you are a 30th level and don't have +6 weapon, you will lag 6 points behind the number you are supposed to have. If you reduce (at 30th level) the PC attack bonus and monster's defenses by 15 each, you will still lag 6 points. Mechanically nothing will change, the chance to hit will be identical.
However, under 4e, your +6 bonus is only a fraction of that +30 you have from other sources, while under those proposed rules it is +6 of +15 or something similar, making it look like the bonus matters more (while in reality it doesn't).
You could state that players lose the +1/2 level bonus, but gain +1/5 level bonus on attack and damage rolls with appropriate weapons and implements and to defenses with armor they are proficient with. Then you remove bonuses from magic items. I don't know if I like that idea but at least it almost completly removes magic item dependency.
That's a pretty common, and semi-official-but-not-really house rule for low-magic campaigns; ditch the enhancement bonuses and give +1/5 levels to defenses, attack rolls and damage.
One. It will tend to shift existing (that is, written without this rule in mind) challenges toward a single difficulty. That is, previously easy fights will become harder (since the party lost more from the D20 than the monster/skill challenge lost from the DC), and previously hard fights will become easier (the opposite).
Yes. And I personally see this as a beneficial thing, as it broadens the acceptable level band and gives the DM more options to throw at PCs.
Two. It will make writing new creatures and challenges more difficult. Currently, if you write a new monster, you have some padding in the design process. If the powers you have chosen are a little too good or too bad, the fact that the creatures attacks and defenses vary so aggressively by virtue of the simple level math smooths it out. Taking that away, even only by half, makes the balancing act that much harder.
I disagree, for basically the same reason as with magic items above: Changing a monster's attack bonus or defense is going to have virtually the same effect with or without the level-dependent bonus.
Three. There will be weird fringe effects. What about truly fixed DCs, like wall climbing and gap jumping? High level characters no longer improve at these. Unless every wall now has to have a level as well as a DC, in which case, the higher level you make the challenge of the wall, the EASIER it is to climb (since it starts at a fixed DC, and you subtract half the level). DCs set by tier (such as monster lore, trapfinding, lockpicking, and so on) will have a "sawtooth" style plot of success chance based on the level of the device/monster, where, for the same character, it will be EASIER to pick/find/learn about higher level challenges than lower level ones, for the same character.
That's actually, in my mind, one of the best things about this. As I said, I hate the skill system and scaling DCs as they stand now. I think static DCs should be static. Why should the 30th level wizard who can't dance to save his life get a +15 to acrobatics?
This doesn't remove skill advancement, skill advancement was never there in the first place. It was all an illusion. If you want to advance in a skill, train in it. If you want to advance farther, focus in it. At that point, you've got a +8 bonus, which is pretty damn good when you're talking about static DCs which will usually be in the 10-20 range.