We seem to differ abit on our views here. Ive never used alch/enchant loop and never will - because I consider it cheating. This is because the loop can make you invulnerable by more than doubling your power. Such a gigantic jump in gameplaychange breaks the game and can thus not be justified by it being neither intentional, logical or reasonable.
However I have no qualms about using necromage. Simply because I dont see it as cheating from a logical standpoint. The perk does EXACTLY what it says, making spells 25% stronger on undead. You are a undead (if vampire), therefore it is legit - EVEN if the developers did not intend people to benefit from it in that way. Necromage only makes stuff 25% more effective. This is not a gamebreaking modifier. Therefore it may NOT be intentional, but it is both reasonable, logical and does not break the game.
If you go by the logic in your first paragraph, Enchanting by itself is cheating because it can more than double your damage and make you virtually invincible without any use of Smithing or Alchemy.
As for your second paragraph, while there is a good argument for spells that you cast on yourself like Ebonyflesh and Invisibility being intended to be affected, and you can
maybe apply that to self-made enchantments, but there's really no logical reason why things like Dual Flurry which are not magical in nature (going by the setting and common sense, not game mechanics) or effects that you don't cast on yourself like the Standing Stones should be affected, and it's obvious they weren't intended to be affected.
But I do agree that looping, and even just combining Smithing and Enchanting, drains the fun out of the game for weapon users. I do occasionally use it on mages, but only to get enough cost reduction on 3 pieces so I can use a unique item or two while still having a high amount of cost reduction. Other than that, looping really does not offer much benefit to mages over what they can get from normal Enchanting.
To clarify, I don't think there's anything wrong with using an exploit. But pretending an exploit isn't an exploit is just silly.