Yes, but imo take the RER instead of a taxi. Unless they are on strike, it will be more consistent because there is no traffic to deal with. You can go from Charles des Gaulle airport to place Charles des Gaulle (which is where the Arc de Triomphe is) with one connection, which should take between 40 and 50 mins on RER B and A. You could go there, walk down the Champs-Élysées, grab breakfast, and continue on through the Tuileries gardens and down the Rue de Rivoli until you get to Chatelet-Les Halles and go back to the airport. Should be doable to get back to CDG two hours ahead of your flight, if you don't spend too long eating.

The AF lounge will let you in for that long because you're connecting, assuming of course you meet the requirements for free entry. I don't think they let you do it if you have to buy entry.