Cash is the most reliable money to buy goods. This is certified by our governmet to be used in buying goods that people needs. The value of cash is from the treasury of one country. Most of us are working for money to fulfill those basic needs to be able to live.
Why people like us are earning bitcoin? Why we mine bitcoin? Because of the value of bitcoin that can be exchange into cash. Cash is secured than bitcoin.
Cash is only more secured than bitcoin in terms of the value because it is fixed and it can't be changed anytime but if we are going to talk about the potential of bitcoin compare to cash then it is clear that bitcoin is better than cash because bitcoin can help you to gain more cash while cash is it is what it is, you can't do much about it but to just spend it.