You haven't complemented Pena on anything. You've tried to discredit him based on his streakiness, and lack of plate discipline.
The problem I have with your post is the glaring contridiction you stated. You ultimately stated that Cano's plate discipline is acceptable because he doesn't strike out. But you had orginally stated that Pena's undoing would be his lack of plate discipline. Why would Cano be spared of that erosion, while Pena would be afflicted with it? Power hitters, do strikeout more than slap hitters. Look at A-Rod he fanned 100 times this year, only in rare cases do power hitters not strikeout.
Pena, is only 24 years old, and has time to develop. He pounded 46 HR's in only 647 AB's. I'm not an expert, but anyone with that kind of power potential is certainly worth taking the risk on. Especially for a 29 year old pitcher who can't control his fastball, and had a K/9 rate of under five.
Even if Pena's plate discipline doesn't develop, he's still a .260/.320/.540 hitter. I'll take an .860 OPS.