I disagree about the energy not being meaningful, but I'm talking about head shots that are maybe just catching the edge of the brain but aren't instant kills.
Most, but not all, rabbit head shots with my .20 using FTT's the pellet can be felt just under the skin or imbedded in the skull exit side (sorry that was gsxrman not you)
And while .177 may be "flatter" shooting it is not "flat", it still has (according to chairgun) about 1.5" drop at 45yds (using my set up parameters), .20 is 2.75" so any shooter that can adjust for one can adjust for the other
But yes accuracy is king & both my .20's are superbly accurate.