For me, we where at our best with Rose and Walker at full back. Their ferocity, athleticism, aggression, pace, power and most importantly abilites as defenders where perfect for us. We're just not the same without the pair of them. Trippier is a bottom half standard full back in terms of his defensive abilites and gets skinned in one on ones against pretty much everyone. Even his his crossing hasn't been that good this year which is literally one of the only things he excels at. He has no pace, can't defend and is not physically imposing.
I think people have short memories. When Rose and Walker were at their best I don't recall many saying "we need to replace them with Davies and Trippier". It was only when Walker was about to be sold that people started to change their opinion of him. And a lot of people changed their opinion of Rose after his comments at the beginning of last season.
I have nothing against Trippier, Davies, KWP or Aurier, they are hard working, honest pros (Aurier's off field issues aside) but we need better if we are going to close the gap with Emirates Marketing Project and Pool.