So, to be clear... you've created a character which is Small and therefore should ordinarily have the lower base movement but in fact is not getting that penalty. To offset this, the proposal is that the player starts off wearing a cursed belt which therefore cannot be removed and thus eliminates the option to make use of that item slot.
I would say it isn't much of an offset. In early levels it seems unlikely they would be making use of that item slot anyway. Later on they would presumably have access to 'Remove Curse', could remove the belt, keep the speed boost (however it came to pass) and now can wear proper belts in that slot.
The thing with a Race is that it's supposed to simulate how it interacts in hereditary factors; in other words, genetics.
A 'cursed item' shouldn't have to simulate a template or racial effect of a creature that doesn't already have it to begin with, especially when by technical RAW (and RAI interpretation) the 'curse' is already simulated by the templates applied to the race in terms of race points.
Should there be a custom item that allows a player to remove this 'curse'? Sure, I don't see why not; infact, it would be a really cool item. Should an item have to simulate something that a racial trait already covers? No, and is also adding a detriment that, unless providing something further to the curse than what the racial trait templates list, shouldn't be added in the first place.
Just to clarify: A) Is the belt making the character small? Or, B) is the cursed belt just something to something to balance being small?
If A) then I'd say that it isn't much of a curse. For a strength based melee character it is a curse, but for almost any other character being small is a great bonus.
If B) then it is pretty much the same. Loosing the belt slot doesn't matter much, unless you are are martial character.
Small size is a benefit to pretty much every build except those depending on brute force damage. Better AC & better attack bonuses are nothing to sneeze at!
The reduced movement speed is one of the costs for those benefits.
No, I don't think the (removable) belt makes up for ignoring cost/benefit exchanges built into the system. Not even close.
manuever builds benefit from larger size as well, as do reach based lockdown builds.
Think about what it is you really want (a disadvantage for a short race that is not slow movement) and then make that a racial trait.
Beltless - Shorties have small waists and do not have the belt item slot.
No need to worry about curses or whatnot.
Halfling, Goblin, Kobold, and Grippli. 4 small races that at least have an option for fast speed.
You don't need anything to offset the small+fast speed.
