There is nothing that suggests Semedo is a better defender than Roberto. Play Roberto in yesterday's game and he would have performed just as good since it was in the Camp Nou against weak opposition.
Roberto gets turned out by pretty much any winger with average to good pace he comes up against. You don’t need to be particularly observant to have noticed that surely?
I’ve seen Semedo have a tough time against Vicinius on one occasion, but by and large he is very good in 1v1 defensive situations. His positioning can improve (though Roberto’s is pretty bad anyway), and his final ball still needs work, but I really don’t understand why people do not view him as a very promising, all round modern RB.
He is fast, athletic, good technically, can dribble - so has the foundation to be a very good FB. Aside from Kimmich, who doesn’t even play the position anymore, I’d struggle to think of many who would come in and do an obviously better job. TAA has horrible positioning, throughly admittedly has an excellent attacking output before anyone mentions him.