The Fast and Easy Wise transfer fee is higher because you can top up wise using a debit/credit card. This is not the case with Monzo because you are using your bank balance, so the transfer is equivalent to the Wise ‘Low Cost Transfer’.
Monzo should fix this, otherwise it will always make sense to use Wise directly rather than use Monzo. This used to be the case previously with the old Monzo interface I believe.