I am not trying to be snarky, so I apologize if I sound that way; I am just trying to understand. So what you are saying is that the feat does not do what it says.
(Emphasis is my own.)
Artificer Knowledge is a specific ability that grants a +2 UMD and increases the caster level of the item being used. The additional enhancements seem to state that you get Artificer Knowledge for Potions (I), Wands (II), then Magical Arms and Armor (III). So if I understand you correctly, you are saying the enhancements only let you use artificer scrolls and wands with a higher caster level. That just doesn't sound correct to me. Especially since the part about the effective caster level increase is a separate "Also..." sentence.
I believe what the enhancements do is grant you the Artificer Knowledge ability for a new type of item with each enhancement upgrade, i.e. a +2 to UMD checks and at least a +1 increase to caster level when using such items. That seems mostly clear although the enhancement descriptions don't use the game term "Artificer Knowledge" like the feat does, only the general term "knowledge." Still, that seems to imply that you are indeed supposed to gain Artificer Knowledge for Potions, Wands, and Magical Arms and Armor when you take the enhancements.
The part that seems most unclear to me is how high the caster level bonus goes. If it stays at +1 for all item types, the +1 caster level for scrolls (and potions, wands, and magical arms and armor) being limited by Intelligence seems redundant, since Artificer Dilettante has Int 13 as a prerequisite.