The transaction rate is not what matters; what matters is the energy spent per transaction. Visa process many more transactions for much less energy than Bitcoin, and is therefore more efficient. I suspect Western Union's energy consumption is roughly in proportion to Visa's, but I have no data (the Visa example comes right out of their annual report, which covers both the number of transactions and amount of energy consumed).
"The electricity spending of miners doesn't determine the value."
The energy cost determines the transaction fees. Higher transaction fees make Bitcoin less valuable by imposing a greater burden on using the system. Yes, there are other factors that determine price of Bitcoin, but if nothing else changed ("all things being equal") then volatility in energy prices would trigger volatility in transaction fees and thus volatility in Bitcoin's overall value.
