While I suppose Deledio has yet to fulfill his ridiculously high potential, I wouldn't call him mentally weak.
And I think no matter what club he goes to he will still be a "big fish."
Think two or three years from now when deledio is 27, 28. Who at Geelong would be better than him? Joel Selwood and that's it. Where if he stayed at Richmond in three years his midfield associates will be Dustin Martin and Captain Cotchin
I define mental weakness as follows:
How many times when the pressure is on have you seen Deledio go missing. More than the alternative. I'd say 9:1 times in fact.
More tellingly, how many big games has he folded in?
Knighter turned around more games for us in a season than Deledio has in his entire career.