Hmm, I think it's fairly well accepted that contract negations can be a distraction for players and that can lead to a drop in performance, that though is a generalisation, and has no dependence upon the means by which negotiations are handled, that'd be more an individual thing.
Having said that you're basically arguing correlation = causation in the first instance, which I find rather weak, and in the second instance you're being a tad selective.
By which I mean in his previous negotiations it was reported that the club lowballed him at the beginning of the season and he chose to reject that to prove his worth. A worth it seems that despite the bruhaha both parties seemed to find agreeance on.
So again, where's the damage directly attributable to Gutho's side of negotiations? It f**king isn't f**king there f**king!