The op's question is a matter of deciding how far you want to travel back. There's no doubt Everton not being able to compete in European competition after Heysel certainly set us back somewhat. You could argue that Everton was set adrift from the big players when the sky premiership league was founded shortly after this. Then there was the era of Kenwright, very much a time of managed decline and reduced expectations. Up until this point, questionable decisions were made on and off the field.
However in my opinion the Moshiri legacy will always be remembered for being an absolute s*** show of the highest order and here's why:
There are clear divisions in the boardroom, all members of which haven't been to a game in god knows how long!
Impulsive player purchases of over-priced, second-rate talent the likes of which have been incredibly difficult to get off our books.
An impressive collection of managers dismissed and paid extortionate amounts of money in compensation.
A flagrant disregard for financial fair play rules and regulations.
The recent fire sale of all our best players and young talent and replacing them with dirge!!!
The relegation fights for the last two seasons.
So for me, it's deffo the MOSH era all the way.