Over the course of maybe 7 games against Stoke x2, Liverpool, Burnley, Arsenal, Everton, West Ham he probably missed 10 chances that he should have scored, whilst scoring twice. There is no doubt that we'd be 6-10 points better off if he had his shooting boots on during these games. The problem for me isn't even that he went through a dry spell, that happens to all strikers. It's that even when we are winning he's missing simple chances. Against Leicester he should have gotten on the score sheet, against Watford he should have scored twice. In the games against West Ham, Middlesbrough, Sunderland, Spurs he also missed good chances.
I have no problem with posters who believe that his other attributes more than make up for his poor finishing. If someone argued that he bullies defenders, creates space and chances for other players; which more than make up for the fact that he's a poor finisher; then we could have a good debate (no striker has everything). However it's the fact that some posters make statements like the bolded - if you accept that missing big chances means costing us then you have to admit he's cost us in several games thus far.
I'm also not saying that in those 7 games he should have scored every single one of the 12-15 great chances he had; or that he should have scored 2 against Watford, 1 against Leicester and 4 or so in other games. It would be ludicrous to suggest he should have scored another 20 PL goals. However he should have scored another 4-5 as a bare minimum, which as a % of current goals is another third.
The stats in the PL suggest this as well for all goal scorers on 10+:
Defoe - 37 shots / 22 on target / 14 goals - 38% shot to goal ratio (28% excluding penalties)
Mane - 33 shots / 21 on target / 11 goals - 33% shot to goal ratio (33% excluding penalties)
Lukaku - 51 shots / 33 on target / 16 goals - 32% shot to goal ratio (32% excluding penalties)
Kane - 46 shots / 28 on target / 14 goals - 31% shot to goal ratio (24% excluding penalties)
Costa - 52 shots / 31 on target / 15 goals - 29% shot to goal ratio (29% excluding penalties)
Sanchez - 64 shots / 37 on target / 17 goals - 27% shot to goal ratio (25% excluding penalties)
Alli - 44 shots / 24 on target / 11 goals - 25% shot to goal ratio (25% excluding penalties)
Hazard - 42 shots / 24 on target / 10 goals - 24% shot to goal ratio (20% excluding penalties)
Ibrahimovich - 76 shots / 42 on target / 15 goals - 20% shot to goal ratio (19% excluding penalties)
Aguero - 60 shots / 33 on target / 11 goals - 18% shot to goal ratio (14% excluding penalties)
Essentially he's been the second worst finisher in the league including and excluding penalties. If his conversion ratio was the same as Mane he'd have scored another 10 goals this season in the Premier League. However more realistically even at 25% you're looking at another 4 goals (potentially 8 points). No-one is saying he's the only one at fault (Pogba, Lingard & Mkhitaryan should also have done better); but he has been culpable.