Iron Skin/Mirror Shell VS Conditioning and Possible Balancing?

Let me start off by saying I'm not a pro player, I haven't even gotten into ranked yet as I'm trying to expand my champion pool and get ones I enjoy playing. However, something I've seen and that makes sense to me is Conditioning seeming to out-class the other two options in the rune group (Iron Skin and Mirror Shell, obviously). While Iron Skin and Mirror Shell provide their defensive bonuses immediately, conditioning provides much more after those 10 minutes. Not only does it provide more base defense (8 instead of 5 or 6), but it provides both.

The real issue here is that the percentage of bonus armor or magic resist is 5% on all of them, but that 5% barely does anything until you've built a few defensive items. By the time you've built enough items for the bonus armor or MR to really be felt, conditioning would have already come into effect and provide a better bonus for both stats. This is all without mentioning that Iron Skin and Mirror shell only activate when you've healed a decent amount or used a healing consumable. Late game when that 5% makes a difference, you'll have probably sold your potions to buy items that make a bigger impact, so this limits the number of champions who can effectively utilise Iron Skin or Mirror Shell.

As I said though, I'm not a pro player. Maybe getting Iron Skin or Mirror Shell can allow you to withstand the pressure from a lane bully and stay in the game through their oppressive early game, or let you snowball with the extra early defenses. Generally, though, I find Mirror Shell and Iron skin are somewhat lacking.

In the case this is true and I'm not just out of touch with runes, the idea I have to mitigate this would be to improve the defense you gain when Iron Skin/Mirror Shell are activated so that they make a tangible difference when activated, and even early on. My idea for this would be increasing Iron Skin to 8 + 10% Armor, and Mirror Shell to 10 + 12% armor. While this would be a big jump in strength, the difference in strength will only be about a dozen armor or MR, even in late game. Even if it is a bit stronger than that, it still requires you to heal, limiting when it will come into effect. It also only effecting a single stat means even when it is in effect, you are a fair bit more vulnerable to the other damage type.

So, thoughts? If Iron Skin and Mirror Shell are fine as they are now then please do explain, but it doesn't quite seem that way to me.