You're right the odds reflect on what the bettors are doing.

As for the whole conspiracy by the establishment to 'rig' the odds idea - meh. I don't think people cast their votes based on what the betting odds are do they? Like, someone is thinking 'zomg 5:1? I better bet for the favourite'. If anything having strong odds would discourage favourite supporters from thinking their vote is needed, and make the underdog supporters think their vote is very much needed.

In this case the race doesn't even appear to be close. It's more like 60-40 than 52-48 or whatever Brexit was. Don't see LePen winning.

I am curious though as to how much Trump's buffoonery since taking office has had a negative effect on populist movements in general.