RE: BANK or SPLINTERLANDS?

Just to point out a few things:
Money deposited into banks is insured so the disadvantages you listed don't actually exist. The real disadvantage of having money in a bank is that the interest on your deposit is lower than the rate of inflation so you lose buying power as your banked money goes up slower than prices go up.
Crypto assets should not be viewed like investments, they are speculative and quite volatile. Speculative assets can be profitable but the risk needs to be limited by diversifying.
Instead of comparing splinterlands to banks it would be more appropriate to compare it to stock/bond investments.
A well diversified financial position might include: two or three months worth of banked cash to help through temporary emergencies/loss of income, an investment portfolio between 80/20 and 60/40 stock/bond split based on age, gold equal to 3 to 5% of the value of your investment portfolio, and speculative assets (such as crypto) equal to 10%.
In the 1990s most people were convinced that it was impossible to lose money by speculating on tech companies. Between 2000 and 2002, many of those companies lost 99% or more of their value. Crypto should be viewed similarly. Don't be afraid to take some speculative risk but diversify accordingly.
A good investment portfolio will see an average return of 8% annually which might not seem like much compared to crypto but it is much lower risk and putting some money into that portfolio every month will allow it to steady build up so that there will be enough money there for retirement. Depending on where one lives, investment advise and management expenses may be fully tax deductable so its worth looking in to and speaking with an advisor.