Not all Armor is Armor Suits, but all Armor Suits are Armor. Using both rules, Armor only has to follow the Armor rule, while Armor Suits have to follow the Armor and Armor Suits rules. It's like squares and rectangles.
You can disagree if you want, but if you do, then you have to accept that Armor Suits only follow Armor Suit rules (and no Armor rules), which opens up a huge can of worms. For instance, Armor does not stack (unless specifically stated), but nothing ever states that Armor does not stack with an Armor Suit. If Armor Suit is not Armor, then it would stack with Armor. Likewise, is the rating from an Armor Suit considered Armor for the purposes of encumbrance? The Rule is regarding Armor and Encumbrance, not Armor, Armor Suits, and Encumbrance.
In addition, the rules already assume you're using standard rules regarding armor for Armor Suits, otherwise they would not need to reference the normal Armor encumbrance rules when detailing how Military Armor encumbrance works.
So if you choose to not apply the same rules to both, that's fine, but the rules never actually state to do that (or give any insight into how they are supposed to work with each other).
The best fix I've found to the main issue (being able to fit more into non-armor suits than armor suits) is to make unrated modifications and add-ons treated as rating 1 or their capacity cost whichever is higher. Then again, I feel that a lot of the capacity costs are way to high, especially for helmet mods (you can grab a camera with all your options and tie it to a HUD cheaper than shoving all the vision enhancement in usually).