I have been wondering what is the point of reinforced now that nirn gives better stats why not just add nirn to loot tables instead prosperous and training which are totally useless on end game gear and same can be said about reinforced.
Reinforced isn't useless.
Reinforced adds spell/physical resist based on a percentage of the item's base armor value.
Nirnhoned adds a flat spell/physical resist.
For items with high base armor values, Reinforced is superior to Nirnhoned. For items with low base armor values, the opposite is true.
That said, both traits are generally not very useful, and now there is very little variety or meaningful choice between them.
I disagree you are only taking heavy armor into the formula and leaving medium and light out, this two drop more frequently because there is more of them, either lock traits by weight or add a flat value so it doesn't become useless in a light piece or medium.