Le Pen's party polls strong but has few allies. My guess is that Macron hopes that even with his party weakened, he can form a broad coalition that would keep Le Pen out. I have no idea how likely that is to work.
Yes, I and could also see an alliance between Le Pen and whatever UMP (hard right conservatives that used to rule all the time until Sarkozy drove the party into the wall, for non French people) calls itself these days. So, if indeed the snap election is a gamble to keep himself in power, it's a risky gamble.
If it's a gamble to let them rule and fail, as you hypothesize, that's even riskier. Fash have a way of staying in power somewhat longer than their popular support.
Either way it's not going to be fun days in France for a little while, damn.
France's Macron dissolves parliament, calls new elections ( www.dw.com ) Englisch