I think it is expected that relatively new currencies have a turbulent period of a certain time.
And as for interest, here in the Netherlands it is less than inflation so you loose money (interest on savings accounts is about 1%, inflation is between 1 and 2% over the past years).
Bitcoin has or will have its niche, perhaps it will not be for your savings but sharing money with friends using a bitcoin wallet app is by far the most frictionless paying experience I ever had. I think you opinion is on the spot though... for now.
What are the factors which could make bitcoin less turbulent later?
As for most frictionless exprience: you do not need new currency for that. My bank offers 'quick send' functionality in their app, basically you just enter amount and select whom to send money to, that's it. You don't even have to login.
Ok, I don't have this option, transferring between my own accounts is easy (requires a pin code) but transferring to someone else's account requires a separate device + your pinpas + your pincode + scanning the screen with this device + typing a generated code into the computer/smartphone.
It would be more stable with more wide spread adoption, I'd guess if shops were to use it they'd en masse refuse to fluctuate/change prices every day, dampening the trade induced fluctuations.
When/if Bitcoin becomes the world currency, it's price will stabilise to match the global desire to defer the completion of trades (i.e. the aggregate desire to purchase goods in the future). So you might expect to see it go up and down depending on very largescale worldwide trends about purchase timing.
It's entirely normal for interest on savings accounts to be above RPI/CPI inflation. Whether "inflation" is the proper term for those price changes is an uninteresting argument, but it's very ordinary for the basket-of-goods purchasing power of your savings in ten years time to be more than it is now (my (UK) savings account does that, and it's by no means unusual in this regard).
Bitcoin has or will have its niche, perhaps it will not be for your savings but sharing money with friends using a bitcoin wallet app is by far the most frictionless paying experience I ever had. I think you opinion is on the spot though... for now.