Arrenado is a great prospect and will likely be ranked inside of the top 20 overall prospects by many evaluators. That being said the guy just finished a year in High A ball and while very good is by no means remotely ready to tackle major league pitching. Most scouts/experts will tell you that the biggest adjustments players make is when they go to Double A. Arrenado will be in Colorado at some point in 2013, but to expect him to make the club at any point this year is wildly optimistic even under the best case scenario. I do not see any reason to be offended by this as Colorado has no need to rush Arrenado and is better served by letting him develop at a normal pace so when he does arrive in Denver he stays put. Ask Toronto about agressively promoting prospects like Travis Snider. The player's performance and the coaches evaluations of what the player needs to improve upon is very important as well. There are special cases where talent can override aggressive promotions but those types are the 5 tool types like Justin Upton, Jay Bruce, Jason Heyward, and possibly Bryce Harper. Arrenado is a good bat but I doubt many will put him in the same category with the players listed above at this point.
Very few of those players aged 20-21 are ready to contribute full time at the big league level. Be patient and let Arrenado develop normally as it is not a slight for a guy that is young and never made it to Double A to not be expected to make an impact at the major league level by jumping 3 levels.