The payment processor is the party to the transaction whose trust is
least dangerous.
You swipe at the grocery store, what's Visa gonna do, not record your transaction? Why is that the only part of the exchange that you're worried about?
Why is it them you want to stop trusting, and not the POS terminal manufacturer who could be lying about the total on the screen?
Or the grocery store you're buying from who could be selling you poison, or who could refuse to carry out a delivery you ordered after taking your money, or who could mischarge you for the items you bought?
And how is your situation improved by switching away from the payment processor with legal responsibilities and administrative controls, to an immutable system that will never, ever, ever let you get the money back in the event of any of the other parties to the transaction turning out to be untrustworthy, even if a court orders it?
Immutability is not correctness. In fact it is the opposite, because in any system that takes input from the real world, errors are guaranteed, whether malicious or accidental. Eliminating the possibility of error correction from the system decreases it's trustworthiness.
> Bitcoin can in theory transact more volume than VISA while using the same energy as it is now since the block time is always 10 minutes.
No it can't. The bitcoin block size is fixed at 10mb, and they've been full for years.
It is theoretically possible for consumption to go down as people exit the network, but that won't ever happen, because the POW system is inherently a power-consumption arms race. There is not, nor can there ever be, a disincentive from buying more hardware and consuming more power. If you crunch more than the other guys you're going to win more blocks and be financially rewarded. The protocol guarantees that the ROI is always positive.