Re: Powell, yeah he scored half his goals in one game but he also came off the bench for 10 of his appearances. He ended up playing almost the exact same number of minutes as Krishna. Even if you discount the WSW game as a freak outlier, then he still only scored 2 less than Roy and one of Roy's was a pen. Powell got 2 assists, Roy got 3. A 1.5 point difference in rating between those 2 is a bit harsh on Powell IMO
Confirmation bias. Pretty common on here unfortunately.
The stats (pretty much the only objective measure on player performance) suggest that with almost exactly the same minutes both players were pretty even in terms of their affect on the match. Here's some other stats: Powell scored with his head and both feet, Krishna only his right. Powell made almost 400 passes, Krishna only 230; despite this Powell had a higher percentage of passes going forward and less going backwards.
Of course stats can be interpreted various ways, but I find them a more accurate gauge of a player's ability than anecdotal comments from people with obvious preconceptions.