As an American expat living in a developing country it seems very weird to me how backwards the US ACH system is. Where I live now it's the same as the countries you mentioned, anyone can send money to your bank account using just the account number. And it appears in minutes. The banks even offer you an SMS alert when founds arrive and the sender can elect to send an SMS to alert the receiver to check their account for the received funds. Everyone uses it, including many (most?) businesses.
From what I understand, the desire for instantaneous transactions is has an inverse relation with how much money you have. Poorer countries are generally way, way ahead in mobile banking, because in a rich country you are supposed to keep around a month's salary in all your accounts, making transfers less urgent.
The way I understand it, it's a coordination issue - the bigger a market is, the longer it takes for a big change to be adopted by everyone.
Plausible stories are easy to make up. Lots of countries - probably most - with higher GDP per capita than the US have lower latency banking. The US has a large proportion of people who are worse off than the equivalents in many poorer countries, too.
Your perspective describes the underlying issue much clearly than those who talk about "leapfrogging".
The newer platforms (like mobile banking) were adopted in those (poorer) markets because they were cheaper to deploy relative to the technology that preceeded them, and perhaps more importantly, they had less inertia to overcome (against entrenched interests).
That, and how much existing infrastructure there is.
Many places leapfrogged directly to mobile phones (featurephones mostly) because there were little to no power and/or landline wiring present (and attempts at getting such infrastructure in place got disrupted by people stealing the wiring and selling it as scrap copper).
Swish allows to send using an arbitrary number (phone or arbitrarily assigned) rather than an actual account number.
It's also credits the recipient immediately. That's possible since all the participating banks have deposited a number of billions in a mutual fund designed to cover the losses in the case one of the banks runs out of money, and also probably by having an internal account to debit during the day.
They are tranfering money between the banks at one (or maybe a few) standard clearing runs involving the Riksbank, that works more or less like ACH. I think all of them are scheduled in the morning.
All Swedish banks are working onreplacing the payment infrastructure (the clearing. ) It's supposed to be finished in 2024 or something like that.
