given that the amount you are suggesting guarantee the transaction, in my opinion it doesn't,
You are welcome to your own opinion.
I'll stick with the facts.
$3.90 to transfer the equivalent of $20 worth of bitcoin is around 20% premium on the transaction. A credit card charges 3% to the merchant.
Exactly. This is why I would not send an on-chain bitcoin transaction to pay for $20 worth of product or service.
There are multiple ways a business could handle it, but in the end on-chain transactions are very valuable things. Very valuable things are expensive.
I wouldn't use a $14000 diamond to trade for something that is worth $20.
I wouldn't use $14000 worth of gold to trade for something that is worth $20.
I wouldn't use a $14000 car to trade for something that is worth $20.
I also wouldn't use a $14000 bitcoin to trade for something that is worth $20.
Note that the transaction fee is based on what the transaction fee is paying for (space in the blockchain). It is NOT based on the value of the bitcoins you are transfering. So, a 192 byte transaction that transfers 1 BTC ($14,500 worth of bitcoin) is going to cost the same in fees as a 192 byte transaction that transfers 0.00137931 BTC ($20 worth of bitcoin). This is because in BOTH CASES the fees are paying for 192 bytes of space in the blockchain.
The fees system was designed by Satoshi to INTENTIONALLY DISCOURAGE use of bitcoin blockchain transactions for smaller value amounts. This makes sure that there is always space available in the blockchain for the transactions with the highest value to byte-size ratio.
This was the intended design from the beginning. Your choice is to create smaller transactions, pay higher fees, or leave bitcoin to those that are willing and able to create smaller transactions and pay higher fees. This is what the whitepaper was created for. This is what Satoshi's code was designed for. This is how bitcoin always has worked, and always will work.
I'm sorry, does the whitepaper say bitcoin is a digital diamond or does it say it's a digital cash?