​Justin Herbert was the sixth overall pick in the 2020 draft. Photograph: Brooke Sutton/Getty ImagesJustin Herbert is one of the most promising quarterbacks in the NFL. In fact, Justin Herbert has forever been one of the most promising quarterbacks in the NFL. That adjective, “promising,” continued to be load-bearing on Sunday, as Herbert and his Chargers turned in an underwhelming performance in a 26-14 loss to the Raiders. Los Angeles are now 0-2 on the year, with those losses coming to the team that just picked No 1 in the draft and a moribund Arizona who picked No 3. Stockholders in Herbert’s growth were taking a beating in after-hours trading. But, as ever, there’s plenty of reason to debate whether Herbert underachieved or whether his team let him down.Herbert is 6ft 6in, can run, has a golden right arm and is capable of making astonishing throws. NFL decision-makers view him as roughly the sixth-best QB in the league but also say things like, “He should have more accolades at this point.” Certainly, he should have more wins this season, but on Sunday the 28-year-old found himself outdueled by one of the league’s senior citizens in Vegas quarterback Kirk Cousins, who is 10 years his senior. Herbert completed 15 of 27 passes for a touchdown and two interceptions, and he also took three sacks. Cousins threw a pick and took two sacks but was much more efficient from down to down (8.7 yards per attempt to Herbert’s 7.1), and the Chargers offense mostly sputtered. In 13 possessions, Los Angeles put together two long touchdown drives and otherwise didn’t march more than 30 yards in a series.Related: NFL roundup: Bears QB Caleb Williams carted off in loss to Vikings; Saints stun Ravens How much of this is Herbert’s fault, though? It’s an eternal question, and one that came up after the Chargers’ playoff wildcard loss to the Patriots last season. In that game, Herbert played miserably but arguably had no chance not to be terrible, because the New England defenders were in his face all evening. In almost any Herbert loss, one can easily find examples of his teammates letting him down. Sunday was another good example. Herbert wasn’t terrific by any means, and given his billing, he’d ideally be able to get over failures by his teammates. But there’s not much the QB can do when tight end David Njoku bobbles a catch on an ever so slightly underthrown ball and turns it into an interception. Or when an under-pressure Herbert throws a ball that either of two receivers could catch without a problem, but one cuts off the other and drops it. Then there’s the injury luck – not so much to Herbert, who has generally been durable while playing through a number of injuries – but to those around him. Every year, a key member of his line or receiving corps seems to go down with a season-ending injury, leaving him exposed or without a weapon to deploy against opposing defenses. There are also question marks over the coaches who have