The two 45s just generally become a swept 90. The harsher the turn the higher the loss and two 45s at the same bend rate as a 90 will increase the radius of curvature just by adding the the straight portions of the fittings. Like others have quantified with number the effect isn’t huge and you also get some losses just due to each fitting’s connections so a swept 90 is generally better than two sharp 45s.