He's ignoring the clear decline during the 5 year period by averaging the results out. And I don't agree that the 6th place was an aberration. I would have sympathy for that argument if there had been no sign of decline the previous 4-5 years but there clearly was.
And the last season comparison is far more valid simply because the players (at Arsenal and other teams) are far more similar.
We're going to score and concede more or less the same number of goals and finish probably 6-9 points ahead of where we were last year, to deny there has been improvement is a nonsense. So the decline has stopped, not only have we not declined, we've not stood still either, in fact we've improved. All in a manager's first season at the club with relatively little investment.
You really do need to get over that or risk looking biased and silly.
"Plenty of strikers can score goals," he said, gesturing to the famous old stands casting shadows around us.
"But a lot have found it difficult wearing the number 9 shirt for The Arsenal."
A 'clear decline' would show results getting progressively worse year-on-year over a significant period. Wenger's results don't bear that out at all. The last two league positions were poor (although the one in 2016/17 was offset by a cup win against Chelsea), but the fact that results went from 4th to 3rd to 2nd in the years before that (including two more cups) show the very opposite of a decline. By your own criteria (trophies, league placing and points) the only possible argument for there having been a decline is between 2016 to 2018 - and even in that time we won a trophy!