Thats exactly what he did do.
He backed up his opinion of Wenger not being good enough any more, with the evidence that Wenger isn't good enough any more.
No league titles in 14 years, for a club like Arsenal, is not good enough.
No decent attempts at winning the Champions Leaugue, since the 2006 final, is not good enough.
Failing to address problem areas in the squad and sign adequate replacements, is not good enough.
Tactical inadequacies on the pitch, is not good enough.
If you do not agree with any of that, that is your subjective opinion, and you are entitled to it, but sitting their saying you are right and everyone who disagrees is stupid

........that only makes you look a tit, mate.
EDIT: And obviously your board disagrees, as Wenger has just come out to say they sacked him (in so many words)
https://www.bbc.co.uk/sport/football/43896201