It's an exploit but an optional exploit that nobody has to use.
No, the "alchemy/enchanting feedback loop" method is not an "exploit." The game has items that fortify alchemy. Alchemy has potions that fortify enchanting. It's natural that players who concentrate on alchemy and enchanting would discover the ability to use both to improve each other in turn, and then make much more powerful potions.
Its a design oversight. I doubt they intended for Magicka to mean absolutely nothing when you wore the right gear. Which, like you point out above, isn't even that hard to do, nor does it require enchanting.
No, the "alchemy/enchanting feedback loop" method is not a design oversight. Bethesda obviously made a limit to how good of an enchanting potion you can make through these normal methods: 32% bonus to Fortify Enchanting (not to mention the other types of potion you can make).
However I would say that using the Falmer Helmet + Circlet method of getting it up to 37% is indeed an exploit, because that is obviously using a glitch to make more powerful items. This is exploiting an unintended feature of the game. Obviously the Falmer Helmet + Circlet is a glitch since the same helmet also doesn't count as Heavy Armor, even though it's supposed to be. (Or maybe someone from Bethesda will tell us that this was actually intended? I think that would be the only way I'd believe it wasn't a mistake.)
But 32% fortify enchanting potions are NOT exploits.
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Now, using Fortify Restoration potions to make 2384927% Fortify Enchanting potions... THAT'S an exploit!! Hehe
-=DG=-