The Boulevard des Maréchaux is ugly as fuck.
'The bronze used for the column was the bronze from the cannons captured from the enemy at the battle of Austerlitz."
Lol. There was so much hatred against the Second Empire that Napoleon's phallus was destroyed by Gustave Courbet during the Paris Commune, so that's quite unlikely.
I would rather go to the subway station (RER) Port Royal. Nothing to see there, but that's the place where Maréchal Ney was shot. You will find a statue of Ney on the avenue de l'observatoire.
If you had been in Paris 1 day earlier, you could have visited the salons de l'Elysée, which are opened to the public once a year. The rest of the year, someone is living there.