The distance difference is not very big so your alternative route is probably a good choice. I took variants of it several times to go to the west of France from the Benelux and I was happy with it. On the other hand, by 10 AM, I think the rush hour in Paris would already be over and it's not a big concern in the summer anyway (many people will be on vacation). I also had the occasion to cross Paris (going all the way to the périphérique) coming from the west or south, with no major problem.
What you want to avoid is holiday-related traffic, when the people who live in Paris leave or come back from holiday. According to the official forecast the 2nd of August is going to be the worst day of the year. The Friday (August the 1st) is already marked as “difficult” in the “departure direction” (meaning from Paris, especially to the south of France) but if you are not too late in the day, you might escape most problems.
Note that no matter which route you take, you can expect heavy traffic on the A10/E5, probably traffic jams around Bordeaux, maybe also in Tours, Niort or Poitiers or anywhere where an accident or road works slow down the flow of traffic. Here again, it's advisable to be there as early as possible, before the bulk of the people starting from Paris in the afternoon.
In fact, you should not really expect traffic jams specifically around Paris. You would probably have absolutely no problem reaching Paris from the north but face heavy traffic and traffic jams from Paris or Tours all the way to the south west. If you could manage to leave even earlier from Brussels (hopefully you have several drivers so that some of you can sleep in the car), it would be best, no matter which route you end up choosing.