I think the key difference between France and the USA is that the electoral system in the USA magnifies the actual electoral popularity of the GOP by favouring rural states over Urban ones, and also that the decentralised nature of elections management means that states with a historic legacy of GOP success and contriol can - and almost always do - get up to a quite simply mindblowing array of tricks in order to suppress the vote, and stop people voting - especially BME, young and poor voters. They operate on the simple, but proven basis, that fewer voters = more likely Republican win whilst higher turnout = more likely Democrat win.
To the best of my (admittedly limited) knowledge, nothing even remotely like that goes on in French elections. The FN don't gerrymander left right and centre, or carve a swathe through electoral rolls, or reduce the number of polling stations to farcical levels, simply because they don't have the authority to do so. The Republicans can, and do, do all that, and more.
I agree with you entirely that political strategies - mass mobilisations, grassroots organisation, community activism, industrial action etc - is more important than the limited value of the ballot box, and rejigging the electoral rulebook. However, in the USA it has to be part of the mix too - simply because of all the tricks the GOP get up to.