But in the end, there will simply be no competing against a deflationary currency. When you throw a deflationary currency among inflationary currencies, it starts acting as a black hole absorbing all the wealth in the world.
Exactly, just like how fiat lost out to the gold standard and we're all on the gold standard now.
Transacting in bitcoin is magnitudes easier than transacting in gold, and even USD.
Resource wise, it isn't. Those old batch systems are orders of magnitudes more efficient on a per transaction basis than bitcoin is. A lot of this has to do with the rewards system of bitcoin, which encourages miners to keep adding on more hashing power even when there is already astronomically more than is needed to run the network.
When VISA for example gets enough processors to run its network it stops adding them because there is no reason to keep piling them on, bitcoin miners on the other hand keep right on adding because they want higher returns. Bitcoin's reward system incentivises mining inefficiency. The network could be run on a few old desktops at its current transaction volume, but instead it's being run on untold amounts of ASICS with huge processor farms chewing up money and energy to keep going.
Credit card companies like Visa will need to have excess "hashpower" (aka processing power) in the event of spikes in the number of transactions that are processed on their network. This would result in customer essentially paying excess fees for using the network (in the form of higher prices from merchants) to pay for this idol processing power.