Lack of consistency with several champions base stats

I pretty much refer to all champions that gain permament stat bonuses passively (either from passive or ability passive), usually in % manner. I mean, some champions have stats reduced to compensate, and others don't.

Champions that don't seem to have any stats reduced: Rammus. Gets bonus AD equal to 25% of his armor. His armor is 3rd highest in the game and his AD seems pretty average for his role. Zed. Gains AD up to 25% of his bonus AD. His AD is high for his role (Talon for example have 5 AD less than Zed), and his stats are generally above average, especially for a manaless champion. Vladimir. Gains AP equal to 2,5% of his bonus health and bonus health equal to 140% of his AP. His health seems pretty good for a manaless mage. Twisted Fate. Gains up to 30% attack speed. His attack speed seems to be unaffected. Galio. Gains AP equal to 50% of his Magic Resist. His MR scales with level (though, it was a recent change). Jarvan IV. Gains up to 22 armor and 22% attack speed. Both stats are about average for his role. Fiora. Gains up to 35 AD. She have high level 1 AD and average growth. Tryndamere. Gains up to 25 AD. As above. (I only count the permament bonuses and avoid any conditional ones, hence only the base 25 AD)

Champions that have stat reduced to compensate: Sion. His level 18 health is one of the worst (worse than Sona for example) in game to compensate for his stacking mechanic, which gives him 2 health for every minion/monster he kills - increased to 10 for large minions/monster and champion kills/assists. Cho'Gath. His level 18 health seems to be also reduced, and quite low for melee tanky mage. It's to compensate for his ultimate stacking mechanic which gives him up to 900 health. Kog'Maw. His attack speed growth is low compared to other champions like him. It's to compensate for his bonus attack speed from Q (up to 30%). Garen. His armor is 7th worst in game, to compensate for his W passive effect, which increases bonus Armor and Magic Resist by 20%. Singed. Seems affected to some point, which both his health and mana being a little below average (though, this isn't by a large margin) to compensate for his passive giving him bonus health equal to 25% of his mana. Thresh. His armor doesn't scale at all to compensate for his passive which gives him 0,75 AP and Armor per soul collected.

There are probably quite a few I missed, but you get the point. There seems to be no consistency in this. I suppose I can understand why infinitely stacking guys have reduced stats, but I see no reason for Garen to have the stats reduced for example (especially since his W passive works only on bonus armor and mr, not the base one).

Imagine the outrage if Zed's AD would be changed to 55 - 96 instead of current 113 to compensate for his W passive (just like Garen is 7th lowest armor, that would be 7th lowest AD) - I mean their W passives work quite similarly :P.

Anyway, I generally think that champions stats seem to be a mess in general, but this is complete lack of consistency for no reason whatsoever (why not give Singed normal health and mana growth and change his passive to 25% of bonus mana for example? There would be no difference in gameplay and balance, but you wouldn't be lied to when you look for champions by their health).

Mind you, this is not an outrage about balance (oh, the balance in champion stats deserves a whole new topic) but about lack of consistency. And I would like to hear the thought process behind it.