Haaland and Lewandowski missed 65% of their 'big chances' as well, are they not half decent strikers because they also miss tons of easy chances? And no I am not saying Jackson is anywhere as good as those two but just pointing out even the absolute best of the best don't convert all their easy chances, far from it in fact.
Would also point out the chances don't create themselves. Jackson is not a poacher who stands around like a lamp post inside the box waiting for his team mates to make something happen for him, he plays a big part in the build up to get himself into those goalscoring positions to begin with. Replace Jackson with a better finisher who's not as good as Jackson at everything else and the team might end up creating way less chances overall, and thus score less goals even if the striker himself was more clinical.
In an ideal world we'd have a player with Jackson's overall qualities who's also much better at finishing but there are not many of those around the market...
Yes, being a player with good movement or intangible but canny intuition to recognise where the ball will fall to have chances in the first place is a big part of being a forward. So is the abilty to quickly shift a ball to get a shot off, dribble to create your own chance, being blessed with pace or strength etc. These things add up to more shots over players who don't have them. It can better to be a worse finisher but with more of all that if the end result is more goals for you or your team.
Even hitting the 'keeper with a shot that someone else might have not have ended up taking can result in a goal too if your teammate knocks in the rebound. Or maybe the goalie saves your shot but you end up with a corner that results in a goal instead.
Think the jury is still out with Jackson as to exactly where he fits in all of that but it's not always so bad even if he is that guy. The offside goal he scored against City the other week was kind of the opposite, a lack of awareness or intuition.
We'll see out it all shakes out in the end.
Even the fact that he's a poor finisher isn't so established. Not many players consistently perform greatly under or over their xG stats during their career. Son from Spurs is crazily ahead, Nunez has shown to be a long way behind over 2 and a bit seasons so far with Liverpool. Jackson was ahead of his xG in his Villarreal days, he was finishing things off fine then behind a fair bit last season. Could well change back again this season for him.
What we can take from last season is that he was getting on the end of things a lot. He had one of the highest xG per 90 stats in the Premier League, and a lot of the players who did similar also underperformed with their finishing. Could have just been one of those years for him. Haaland, Salah and Calvert-Lewin were wasteful too. Nunez more established in that regard as it's 2 seasons in a row now and he was much worse than anyone else in that aspect last season.