The thing is we don't need a player better than Evans (although it would be a nice luxury). The point others have been making is that it would be great to have another big player in the backcourt to try to make the other team guard Reke with their PG. The simple truth is that if Reke keeps developing, the other team is going to put their best wing defender on him even if we can force a mismatch. The bigger player though would not need to be a Roy/Johnson, but could be someone like Doug Christie.
Another thing in terms of that player being "better" than Tyreke. I mean yes, technically you can argue that we would want a player who is better than Tyreke is TODAY. I mean Tyreke still needs to improve his outside shot, he still makes rookie mistakes, needs to improve at finishing in traffic, etc. But so did Roy, Johnson, Kobe, Lebron, Wade, etc. during their rookie seasons. I know personally, when I am talking about who we need to put next to Tyreke, I am thinking about a more developed version as I assume a 19 year old with a reportedly very good work ethic will improve.