See, I had an idea one time.

There could be a bonus system. +1 would make it one tier higher, +2 would make it two tiers higher, using the armor rating scale.

The bonus is a function of your smithing level + a bit of luck. The "base" bonus function is roughly bonus(level, tier) = floor(5 * log_10(level - tier + 1)) for your smith level and default armor tier. So for example, at level 1 smithing you'll get a base floor(5 * log_10(1 - 1 + 1)) = floor(5 * log_10(1)) = floor(5 * 0) = floor(0) = 0 bonus for bronze armor, at level 2 smithing you'll get floor(5 * log_10(2 - 1 + 1) = floor(5 * log_10(2)) ~= 3 bonus, but at lv 100 smith (master cape bonus) you'll get floor(5 * log_10(100 - 1 + 1) = 10 bonus, so it tapers off but always increases.

Now after you get the base calculation, it would be time for the "variation". Inherent variation causes plus or minus 1 tier (so you could have -1 bonus, which would cause the opposite effect and would basically make t1 armor worthless) - this would represent the smither's skill at making this item, sometimes he makes it better, sometimes he messes up.

Then there's ore bonus, which would have the same system for mining as described above. However the bonus for armor is 50% of the stated bonus from the ore to represent the natural imperfections of smelting.

Then there's a "good luck" bonus of upwards to +5 using the same probability distribution as spicy stews (equivalent negative boosts are just put as 0 bonus so that it's not too unfair one way or the other).

This way, you can get a +20 boost to your armor, but it would be exceedingly rare and the demand for such an armor would be so high that you could sell it for maybe 1m or 2m (t70 smith able armor would now be t90, t90 would be t110), making smithing a good source of money again.

(tbc on my computer)