Lingard may not be a particular skilful or technical player but he does well enough (above average) is most things.
Martial is a much better dribbler but Lingard can still beat a man at speed occasionally.
Arguably, Rashford can finish better but Lingard has shown he has ability to find the net too.
It is easy to scorn Lingard because his Football isn't easy on the eye. But it does appear that he does other things well enough such as being defensively more astute, attacking the space, disrupting defenders etc, better than the likes of Martial, Rashford or Mhiki.
I love Martial as a player, his direct forceful runs are beautiful to see but the problem is without the ball he seems very static.
Lingard most certainly deserves a spot in the team.
People keep claiming he is keeping better players out of the team. That's illogical, if these so-called better players were showing their true value and potential, Lingard would never get a sniff. It just means that these so-called better players aren't stepping up enough, or that there are situations where the manager trusts certain qualities that Lingard has over the others. That's the manager's prerogative.
Honestly this forum is getting worse over the years. There has always been criticism but increasingly there is so much hate and dislike and negative sentiment towards our own players. Support our manager and players and stand behind them. If they are good or bad, time will sort it out.