The game has levels, classes and hit points and ability improved as you go up the levels. Perhaps the road travelled is harder for a Wizard than say a Thief or Warrior?
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I liked that players made a decision to either go for a class that progressed quickly but was ultimately weaker at the higher levels than another.
In fact, in AD&D, a wizard needs fewer XP per level than a warrior to get to 7th level, and needs fewer XP for each level until 14th, which requires 1.5 million for both. The wizard then needs more XP per level gained.
But let's put that to one side.
If a thief takes 1 XP per level and grows half-an-inch per level; and a wizard takes 2 XP per level and grows an inch per level; in what sense is the thief progressing more quickly but weaker? They are both gaining the same amount of height per XP earned, but one is just being divided into more granular units.
It created different power curves and made character choices more interesting.
Sure, but that is completely independent of the XP charts. You could tweak all the abilities per level, and then the XPs per level, to achieve the same abilities accrued per XP earned, and the power curves would be what they are without having differentiated XP charts.
There's a pretty strong case that this is what 3E does!
This does make sense and I think it's how most people view/viewed the game...IMO of course.
But surely you can see the only difference between requiring 2000 XP to get a level conferrnig d4 hp, 1 new spell and +1 to hit, and requiring 4000 XP to get a level that confers d10 hp, 2 new spells and +2 to hit, is that the former is more granular? The two progressions don't differ in power curve.
I also am not so sure about a level not having an in-fiction meaning (though I would argue it's implicit as opposed to explicit) since abilities based in the fiction are very much tied to leveling. In the fiction a level Y wizard can cast level x spells... A level Y fighter has X skill points, a level Y Barbarian can rage X number of times per day... this are all things that are in-fiction and tied to level.
The spells I can see. The barbarian rage is in the same zone as martial dailies - I think different people have different takes. But does anyone think that
skill points are an ingame phenomenon?