Very proven, Yes. Holding bitcoin for longtime proves to be one of the best ways to grow money we have. Very much compared to interest given by bank.
Looking at some famous stories who have been made rich by investing and holding bitcoin, your statement is indeed correct. Banks do not give us as big profits as bitcoin do and that is people are investing in it instead of banks.
This is the main reason why it is a threat to banking system and indeed it is a big one. Bitcoin is just a way to get out of all financial problems and earn enormous money within a short span of time.
That is the most simple and the best statement about this subject. Everyone who merely knew about bitcoin, can assure you one thing, holding will give you more profit. What is the reason behind it? No other than the high going of prices every other time. Prices are fluctuating every time but with little dumps, they are trending to go higher and higher each coming moment.
I hold most bitcoins. But I also use some as I believe circulaiton will make it more valuable.