>Statistically that should be the case 50% of the time.

Only if the risk premium is the same.

>Treasure bonds are liquid, so buying a 5 year one does not mean that you have to hold it to maturity.

Here you claim that the risk premium is the same because it's liquid. However the term is not the same so you'll be hit with a bigger effect when short term interest rates change on a longer time horizon instrument.