The birds did not ask to have invasive incomers eating their eggs and chicks, and the red squirrels did not ask to be outnumbered, outforaged and bullied by grey ones.
The red ones eat a more restricted diet - spruce and pine seeds, acorns, berries, fungi, bark and sap tissue. Grey squirrels will eat these too, and anything else, including eggs and young birds. They are twice as big as red squirrels.
Not a level playing field. It is on a par with letting motor-cycles compete in the tour de France.