That is a very difficult question- presuming that both are at level 10 heat and are supposedly "equal" in terms of price, ancient would have to tank enough damage, or give a worthwhile enough perk, for players to see using it as an option. This is particularly challenging because we do not know how the armor was intended to act-- unless it acts correctly and is supposed to be worthless.

The first way to balance it would be to make it more of what it already is, but better. Give it something like ASI decreased med, MSI decreased med per piece- and then give it all of the specialized defenses at the current level of its normal defense. Something along those lines SHOULD specialize the item enough for players to see it as worthwhile, though it might require additional tweaking to get it right.

The second way to balance it would be to make it into what it should be. Give it something like "knight cannot flinch" or "knight has regenerating health", and it could be made to feel like it was intended, and through that could be made viable for use.

The second way would be harder to get right- too much health regen would outclass even chaos, too little would do nothing. Finding a sweet spot- a legitimate playing style that fits the item- would require a small amount of testing on the part of the developers, before the item is ready to milk the players via the testing server and then further disrupt the current balance of armors in the game. That being said, I'm doubtful of whether the first way would be a legitimate option for the armor due to the way damage reductions work.

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The real issue here is the cost though. Skolver costs a very clear cut amount to make and use; ancient requires a different amount per player, based on skill and existing gear. Under the radiant drought, skolver also has an advantage; it requires no heat to be useful. This would easily be the largest factor when "fixing" defensive items.