You are not considering the involved orders of magnitude.
A baseline for comparison is actual money cost to do something. How much does it cost to print a note, how much to mint a coin, how much to cryptomine a unit of cryptocurrency, how much to transfer said cryptocurrency to a new owner.
If you switch to a trust-based wallet system only representing the actual currency you lose all benefits from the cryptocurrency concept. You give control to the wallet company. Effectivly you would exchange transfering intangible online money to transfer intangible online creditpoints. The problem is, that the value that those creditpoints represent have no value at all (actually they represent how much heat you generated by burning other money to pay for your power bill). The value of cryptocurrency exists as a want to be independent of banking and government control. If you shift that to companies, those companies have to comply to laws of the govs they want to operate in. And they will have to act as banks. But to work as intended, the crypto has to be decentralized and independent.
Part of the mining is making transactions happen. Because for the currency to be safe, it has to be not cheap in computational power. There is actually a very deep flaw in design, that you could take over a currency, if you provide 51% of computational power.
All that being said, it is prohibitive to use crypto for small transfers. Just as it is prohibitve to mint 1 cent coins to pay for a car. The cost of say a dollar bill ranges about 5-10 cents and that bill has a life expectancy of 6-20 years. The cost of transfering money is in the vicinity of less than a dollar and a percentage charge. So lets say 30 cent for a dollar and 1 dollar for a 100 dollar transaction as upper bounds.
3 years ago the cost to make a transaction in bitcoin was around 300 bucks in power cost.
As an investment it is too volatile, meaning, yes, you can make a fortune - or lose everything. As a money concept it fails miserably. And please do not compare it to projects like protein folding. Those protein folders do not sweep the market empty making my graphics adapter triple in price, because they put them in display-less computers running them 24/7 "mining" value. They do not mine value, they mine hot air certificates. Quite literally.