It is not a problem when one player has bad season, Salah more than covered for him that time and both Trent & Robertson were unstoppable. When you have the results, players aren't under that kind of scrutiny. This season most Liverpool players are under-performing and results show it well. Then media starts taking them apart one by one since that is what sells the papers
Mo Salah is only one player in a system so his performance will be affected by a whole team. If a system runs well, he will get good support and get benefit from it then he has a better performance. If a system has issues like Liverpool have in this season, he will be affected negatively.
A single player is almost impossible to carry a whole team like Plantini, Maradonna a few decades ago. Nowadays, in modern football, it is a game of system and tactics and even a super star player has to get enough support from a coach and other players to show his best performance.
Salah did try his best and still shown his high ambition but he needs more support from Liverpool midfielders and swing backs.
Nobody would talk abut bad defending if Liverpool outscored their opponents with results like 6:3, they would be speaking about playing football for supporters and always looking for a goal more.
Yes, it is the same for Barcelona in golden era with Pep, Messi, Xavi, Iniesta, Busquet and other players. They did not have a strong defense in those seasons and Victor Valdes is not a best goalkeeper in Spain and La Liga. He just got benefit from Barcelona's high ball possession and domination so that he won 5 Zamora titles. He won it even he was not the best choice for Spain's goalkeeper in World Cup or Euro.
Zamora Trophy: 2004–05, 2008–09, 2009–10, 2010–11, 2011–12
[1]
https://en.wikipedia.org/wiki/V%C3%ADctor_Vald%C3%A9s