re: No, not really
You would probably be right if all plastic bags were made from recycled plastic, or all paper bags were made from non-recycled paper. In real life, neither get recycled much. In any case, a million years from now there will still be trees.
Those who tread lightly on the earth bring their own washable hand-made hemp bags to the grocery stores while snubbing those poor peons who don't have the time or money to do this.