Why is oxidizing power of #F_2# higher?
Because the fluorine molecule is the most potent oxidant on the Periodic Table....
Fluorine is such a potent oxidant that you cannot perform laboratory scale reactions, unless you have special equipment and conditions. And it is a fact that many of the older fluorine chemists have missing eyes or missing fingers because of the supreme reactivity of difluorine.
Fluorine will oxidize most every element on the Periodic Table....and its position on the Periodic Table reflects this....i.e. it has high nuclear charge, and readily accepts electrons from other substrates....