We may not have good measures for estimating Fb or Lb let alone Lc, but the Kepler mission gives us a pretty good estimate of Rb. You should update your estimate of the closeness of a biotic planet depending on whether your Rb prior was higher or lower than the result.
That is true. However, if "any value could be assigned to Fb", then any value can be made to come out of the Drake equation, except for an upper bound. Updating on Rb can shift around that upper bound, but it tells you nothing about the really small values that decide whether we are alone in the universe or not.
On the abundance of extraterrestrial life after the Kepler mission Amri Wandel
Some recent calculation of the Drake Equation with estimates of the likelihood and logevitiy of civilizations
Related: The Great Filter and Planets in the habitable zone, the Drake Equation, and the Great Filter