I have to wonder whether the increasing difficulty of the presidency may have been one of the reasons for Bush's and now Obama's poor performance and reputation. It may indeed be too much work for anyone to do well.
The article seems to suggest that it is rather the result of a press looking for short-term advantage over their competitors and an uneducated populace who listens to them. I think that it is true that increases in lobbying and decreases in bipartisanship have reduced the ability of much of the American government (not just the presidency) to get things done, but I think those issues would be mitigated if more of the voting population was willing to delve deeper into legislative issues. Soundbites might be easier to digest, but they are also less filling.
Could it be also, that the government is now involved in too many aspects of daily life? Education, nutrition, employment, regulation at a micro economic/firm level and economic development are some areas into which the government has expanded.