2 years on from a Golden Boot season is a long time.Porro is a defensive liability. On a large club in another league (especially La Liga), he'd be a great player, because they don't need to defend like they do in the Prem. For me, he's actually looked a bit better defensively since Romero has been out (so maybe it's the the combination of the two on the right that's the disaster), but still not good enough. I think he'd be good to keep as a backup at the wing and wingback, but I can't imagine he'd accept that role. Vicario makes too many mistakes, and is a pushover in the box on set pieces. He plays like he's 5'6 and 7 stone. I think it's relatively well known that Forster is past his best, and he's been much better than Vicario. As for Son, he's done enough in his career for me to afford him some time to get himself together. It's not his first slump, but he's only 2 years removed from a Golden Boot season. Maybe he could be in the "But need(s) to do better" group, because he certainly hasn't been his usual self this season.
Crucially, Son has lost pace.
Vic is exceptional in some areas, and yes needs to improve on crosses and set pieces, but there were some signs of improvement pre his injury. TBH there isn't a whole lot between him and Forster net, but obviously Vic is younger.
Agree that Porro further forward is an interesting idea.