I'm still totally confused why I do not have to enter CPP Taxable benefits from T4A (P). does this not grossly affect my taxable amount and thus get a larger refund?

Are you referring to Box 20 - Taxable CPP Benefits? You don’t need to enter the amount that appears in Box 20 of your T4A(P), because when you enter in the amounts in Boxes 14 to 19, the program will just calculate Box 20 on its own.