I am not an expert in Magic, so I can't speak to specifics of individual card sets, but I can say that no single designer or developer has the power to tank an entire line of any kind of product at WotC, be it RPGs, novels, Magic, or otherwise. Perhaps the Director of all of R&D might share some of the blame for problems, but even then, there are a lot of people that are involved in decision-making, including brand management, technology, finance, Hasbro, and so forth. I will be the first person to tell you when I have no idea what's going on, but I do know what I'm talking about on this matter.
I may not be a MtG expert, but I do know Tom. I know that he deeply cares about the health, future, and success of the game. I also know that he is very passionate about RPGs. He is one of the rare breeds of designer who has equal strengths in both the mechanical and the story-driven aspects of RPG design. And he is not only knowledgeable about and interested in D&D. He has other areas of interest to draw from, such as his background in martial arts, knowledge of Asian culture, and interest in philosophy.
I think Wizards has a very capable person joining RPG R&D in Tom. I think we'll see great things from him.