Armor can be balanced by using different degrees of protection against different forms of attack (blunt versus blade), by using weight to reduce the effects of Agility and make some actions harder in armor, by varying repair cost and difficulty, and by making some forms of armor more or less durable than others.
You can have an armor type that's initially very protective, and is light enough not to hinder stealthy movements and acrobatics, but is brittle and breaks after a few hits, and costs quite a bit. An assassin would love it, where they're not expecting to engage in multiple combats, but need to survive one fight against a competent enemy. It won't hold up well under constant use, however, and costs a mint to keep in proper condition.
You can have another type that's quite protective, holds up well under repeated abuse, and is moderately easy to repair, but weighs a lot and tends to limit your ability to jump or sneak. The wearer is often described as a "tank".
Another type can be significantly less protective, but takes very little damage itself and is easily repaired with minimal cost and skill, making it preferable for long ventures into the wild where other "superior" armor types would fall apart without regular maintenance.
You can also have cheap armors that offer moderate protection, moderate durability, and moderate weight, but only limited repairability. When they get worn out, it may be cheaper to replace than repair.
With those distinctions or something like them, one armor "skill" is sufficient. The armor itself provides the diversity and freedom of choice, rather than relying on skills and perks to offer distinctions. Normally, I'm all for more skills and more options, but in this case, having multiple armor skills really doesn't make a lot of sense. If the heavier armors create more of a problem for agility and speed, while armor skills help negate the penalties, the character can either choose lighter and less restrictive forms of armor, or increase their armor skill to reduce the penalties at the cost of not increasing some other skill instead. Heavier armor should be a choice, and trying to do agile and fast actions in heavy armor should require a lot more training and effort, not that it can't be done. That also doesn't require dividing armor into distinct and sharply divided "heavy" and "light" classes, when there's a whole lot of "gray area" in the middle which the system won't cover. Individual armor stats can cover all of that and more.
The absolute last things I want to see are either another mindless equipment rat race where each level effectively becomes "Armor + 1", and you always have to get the next new and "better" thing, or an absurd stat-free system where it really doesn't matter what you wear, because heavy plate armor gives the same protection as a thin leather vest. Either way is an absolute killer for RP, where you would generally choose to wear whatever makes sense for your character and situation.