Why the three-centre, seven-defencemen idea makes no sense

With offseasons come lineup blenders, and with lineup blenders come fun ideas. One of the most interesting ideas, at least as far as sheer uniqueness goes, is that the Toronto Maple Leafs should run three centres and seven defencemen next year. As radical of an idea as this is, the rationale given is pretty simple:

• The Maple Leafs now have three legitimate first-line centres (John Tavares, Auston Matthews, and Nazem Kadri) who are capable of playing a 20-minute share per night, eliminating the need to have a fourth centre at all and making wingers fluid.
• A seventh defenceman would keep Toronto’s six from getting tired, and perhaps allow for someone to dress as a “specialist”, used only in specific game situations where Mike Babcock likes to have certain types of players.

It seems sensible on the surface, but there are quite a few flaws to the concept.