One of the main reasons that Napoleon returned was that the Bourbons failed to observe the Treaty of Fontainebleu and refused to pay Napoleon his pension per the treaty. They broke their word, and without the pension Napoleon could not pay his Guard, who also had to live. The Bourbons made a complete hash of attempting to rule France. They certainly alienated the army and the peasantry, which essentially doomed their resumptive rule. It is the Bourbon's own fault that Napoleon returned at all.
Naming Napoleon a 'usurper' is absolute nonsense and falls into line with British, Bourbon, and allied propaganda of the period.