Yeah. I agree with you that it's intent is to use in combat to take something small if you make the opposed check. However, it's not as good as you are trying to make it out to be. It's a 3rd level ability for God's sake. You can't see into unknown pouches to know what to take, nor can you take multiple objects at once. At best, you get lucky and take something for a significant spell.
You can't see into unknown anything to know what to take. It would be useless if this is how it was ruled. Are you suggesting that any time I take somethuing from any container as described in the ability it is entirely random what I get out of it?
When the wizard casts fireball, he reaches in to his pouch finds the bat guano among all the other things in there and takes it out. You do the same thing- reach in find the bat guano and take it out. Now if I say I reach for the bat guano, and there is no bat guano in there. Well then sure, you are right I don't get anything, but if it is in there and I pass the check I get it. In this discussion let's remember that you are not even letting him lift the whole pouch as was intended.
Think about the implication for other uses if we take this interpretation - I reach into the guards pack and grab the keys to the cell. Well no you don't get the keys, you get the leftovers of yesterday's rations because it is an unknown backpack so it is random what you pull out. Ok I do it again - This time you get a flask of brandy but not the keays. This is the logical interpretation of applying this as you say it should be. It would be a completely useless ability that they spent 3 paragraphs describing if this was the case.
It is also not very powerful for a 3rd-level ability. Many abilities and spells can completely disable a foe that fails a save. For an apt comparison consider:
1. A 3rd-level Rogue going against a caster using a component pouch or who puts his arcane focus away can
TRY to steal said focus or pouch with a successful check, assuming his hand starts the turn less than
30 feet from the caster.
IF the check is successful, the spellcaster can not cast spells with a
material component until he gets it back.
2. For comparison, a 3rd-level Bard or Cleric who starts his turn less than
~170 feet of a caster can cast silence and the caster can not cast spells that use a
verbal component.
There is no save to this, it is always successful.
There are far more V spells than M spells and almost every M spell also has a V. As such it is pretty obvious which of these 3rd-level abilities is more powerful.