If one is to be sold, it should be Roberto.
He is useful because of his versatility, but given there is no position where he excels, someone in the team or out there is better than him in all positions.
Semedo, on the contrary, is a pure RB, who as a RB, and not in general is better than Roberto.
He was misused by EV, has already improved a lot under Setien, and can give more (lOl at people saying he is not good defensively. One of his best traits)
The talk about many RBs out there being better than Semedo illustrates either wishful thinking about young and upcoming prospects or not having a proper sense of the reality of RBs right now. Just try to think who is better than Semedo atm in top teams in Europe. You will find a few untouchable and unsaleable players, a lot that are not better or old, and then nothing of proven quality. Just enumerate some:
Walker? Questionable. Old to buy now.
Trent? Of course. He is worth 100+
Wan-bisaka? Not better.
Hakimi? Maybe. He was just sold, he would never play for Barca anyway.
Who else is there? Pavard? Danilo? De Sigclio? Azplicueta? Menieur?
And then we are talking about Dest and Dest-type players who might turn out good in the future, but are less proven than Semedo was when he came in.
So, after some reality-checking, we see that there are not that many options of quality RBs out there that can play better than Semedo.
There is a reason no one wants Roberto (bar Pep) and there is a reason the only two Barca players that generated concrete interest -when the whole team is for sale bar Messi, Ter Stegen, and De Jong - were Arthur and Semedo.