1. visa takes seconds because they DONT settle the transaction in seconds. they just see you have balance available and sign that funds will eventually reach the shop LATER. visa is like a zero confirm transaction. its signed but not settled. shops dont get the funds until 3-5 business days later. check your bank account you usually see 2 lines. one 'available balance' one 'pending'. then even once the funds leave your account the next day they dont arrive at the shops account for another couple days. and even then are still reversible(chargebacks)

2. originally people could trust zero confirm transactions. but the down side to the core devs decisions of functions like 'replace by fee' and 'child pays for parent' is that some zero confirm transactions can be swapped out even when the network has them in the mempool waiting for confirm. even lightening transactions have this issue where users can abuse the system of replacing out an signed transaction with another before its comfirmed onchain thus changing its amount/destination at a whim. and lets not forget their 'penalties' (chargebacks). so even lightening is not a solid system

3. i do agree that devs have put in stupid loops holes and not bothered fixing issues onchain to strengthen it as thier way of pushing people to use the mainchain bypass (LN), but these devs have been given over $100m to create a system to make corporations money by making blockchain look bad. by saying blockchain is slow, untrusted, cant scale.. (facepalm) and that putting funds into 'managed accounts' (multisig channels) is the only way forward(facepalm)