Except pets and tier 19 weapons, all other items have same probability/rarity. Most NFTs don't have items tied to each other, but heroes do.
For example, let take a look at the Knight class, if you want to get maxed out stats, which is a tier 18 weapon, tier 15 chest, tier 9 helmet, tier 9 shield, and tier 9 boots (18/15/9/9/9), the probability of getting it is 1 out of 196.830, but there are only 2.500 knight NFTs in the collection. If you want a tier 18 weapon there is a 1/18 chance you will get it, but if you now want to also have a tier 15 chest now this drops to 1/270, now add a tier 9 shield, and you get to 1/2.430, and you are still missing 2 parts.
Look at it like a slot machine: if you need to get three 9's in a row, one number 9 on itself is pretty common, but to get three 9's in a row is rare. You can have a tier 15 chest but if your other parts are very low tier, you will receive more damage then some other player with a full mid tier armor set.
Tier 19 weapons are rare items. Users who own tier 19 weapons will have a unique weapon skin in-game and damage boost. Pets are also rare items, in-game they will follow your character and give you bonus stats in P2E, so you can survive longer and give more damage to the boss. Rare items are in the table below:
|25x Black wolf||17x Brown bear||24x Stone golem||16x Green dragon|
|13x White wolf||11x Half armored bear||20x Wood golem||15x Black dragon|
|8x Magic wolf||9x Full armored bear||7x Fire golem||5x Red dragon|
|10x Tier 19 weapon||11x Tier 19 weapon||15x Tier 19 weapon||15x Tier 19 weapon|
If you sum up the tier levels of your Hero's armor parts and weapons you will get your Hero's rank. Hero rank distribution is in the chart below. Heroes that have same overall rank won't necessarily have the same stats in the game. For example you can a have Hero with a high tier armor and a low tier weapon, which would be more of a tank-build hero, if your hero has a high tier sword and a low tier armor it would be more of a damage dealer. The higher the hero's overall rank, the less specialized he is, because he has both good armor and weapons so is a good tank and damage dealer, but the heroes listed in the middle of the chart can lean more specialized towards damage dealer versus tank.