I’ve had bitcoin transactions that literally took several days to process. This was also using an average fee.

I use Bitcoin regularly, this has literally never happened to me. If your transaction took days either you accidentally set a super low fee or your wallet was bugged somehow. Generally speaking the only way an "average fee" transaction takes more than a block or two is if you pay an average fee right before a rare massive fee spike, in which case, you can do a "replacement" transaction by upping the fee or just wait. Look up "average Bitcoin transaction fees" if you want to see rarity and size of fee spikes.

A handful of minutes or hours in a high-fee scenario, btw, is still much faster than ACH or international wires. Even if the money appears to move that quickly with traditional banking, full settlement is often measured in days to weeks, ask any vendor whose had a chargeback or anybody whose tried to "withdraw" from their Venmo right after depositing to it. Bitcoin's main chain and Fedwire (used to settle liquidity between US banks) have equivalent daily transaction capacity.

You can open a lightning channel with a single on-chain transaction. That lightning channel can stay open for years and process trillions of transactions, instantly, for pennies in fees. If you need a transaction done quickly, you shouldn't be sending it on main chain to begin with.

Long-term the vision is for folks to be using lightning or other L2s for everyday transactions, not main chain. Most Bitcoin transactions by transaction count are already on lightning. Lightning has been out for 5+ years now. It works well and gets better every year.