I think Salah has blunted Mane's form largely because Mane was the one giving us penetration last year. He was the ONLY player looking to get in behind the defence and he had Phil and Roberto looking to get him in.
Now Phil has moved back, and Salah is making the penetrating runs, Mane, as Ryan says, is looking more to combine and get in behind.
Also, the first pass the midfielders look for is now Mo, as opposed to Sadio.
That said, I expect when Sadio is back to 100%, whilst he may be less effective in terms of goal output, he will still be our 2nd highest scorer and the team as a whole will be more effective scoring. Scoring 3 against Southampton (a team we've notoriously struggled against) is a good sign of progress offensively.