Great question... I think no striker will ever look good in a struggling team, especially not a target man like Salech. He's certainly been as bad as the rest the last few weeks but the team in general looks to have given up. How much is him vs the the service he's getting is very difficult to judge.
Robinson is an enigma for me throughout his time with us, when he's on he's one of the best off the ball and one of the best finishers in the division, but there are far too many games where he doesn't make an impact at all. I guess I'd say Salech probably has more of a baseline in which he contributes positively to the team, but Robinson when he's playing well is a far better and more impactful player for us.
Can they play together... who knows. A better more experienced manager who didn't go through lineups and tactics like a 13 year old playing Championship manager might have come up with something that worked and stuck with longer than a game or two to give it a chance.