He lost his way because of money. He was a talent as a teenager, he clearly never fulfilled it. Losing his way at Arsenal and being behind Henry Bergkamp et al shouldn't lead to a player not being good enough to play for a championship side or a scottish side.
Look, I'm sure he made mistakes, and I'm not here to judge him, he's almost certainly made more of his life than I have, but I wouldn't read too much in to his comments. He made 292 professional appearances and scored 52 goals. He'd scored 18 of them before he left Everton, aged 20. I can't take it seriously when he effectively says he only scored 18 league goals, over 11 years, in a load of mediocre competitions, because he found it a bit difficult at Arsenal.