Jungle Items (Civil) Discussion

Hello, I was wondering why some jungle items were designed the way they are instead of some other, friendlier way to certain classes. Those 2 would be the Devourer and Magus enchanted matchet upgrades.

As far as I can tell, the jungle items each serve a specific class:

Juggernaut: Tanks/ AD Fighters Warrior: AD Fighters/ AD Assassins Magus: Mages/ AP Tanks Devourer: Auto-attack based champions.

So, here are my 2 questions:

1. Why was the Devourer item made as it is instead of an item tailored towards champions like Yi/Tryndamere/Fiora and Marksmen (zeal instead of double daggers, movespeed/critchance instead of magic damage/scaling damage)?
   Besides supports, who aren't intended to jungle in the first place, why aren't AD carries (Marksmen or Melee) not represented here?
2. Why is the magus enchantment so mana-inefficient? It provides too much CDR for the stage of the game you're in (you drain your mana bar 26.667% faster assuming 5%CDR from masteries) for no extra mana regeneration. If you're going to clean fast, you need to spam and thus you don't get much mana back. If you don't spam, you lose more HP than you can afford to lose in order to jungle and gank. Buying a tear before the Magus upgrade delays all power spikes by 700 gold (game time can vary from single digit numbers to low double digit numbers).

So, I'm genuinely curious, why were these designed the way they are?