How the Magento 2 Final price calculate for the simple product?

So again you have:

1. Regular price -> 100
2. Catalog price rule -> 10%
3. Special price -> 80
4. Tier price when a customer buys 1 item -> 70 (keep in mind that this price is lower than Special price)
5. Tier price when a customer buys 2 items -> 130

Let's start from the end:

5: This means than when customer add 2 items into the cart you want to sell each of them 130 each -> as a result, you have to get 260 (remember this -> when you configure 130 in admin, this doesn't mean that total price in the cart should be 130, this means that you want sell each of them at the price of 130)

4: The same logic as for above -> when you configure 70 in admin, this doesn't mean that the total price in the cart should be 140, this means that you want sell each of them at the price of 70. Why this works ? because 70 is lower than Special price

3: Special price will be applied if it is lower than Tier price, so if you configure it as 60 -> Tier price from point 4 won't work.

2: It doesn't work at this situation at all. Make sure you apply this rule, and everything is reindexed.

1: If you make a regular price, for ex., 60 and a special price 80 -> M2 skip special price and apply regular, as as it lowers than special.

I hope that this explanation makes price stuff in M2 more clear to you.