And first past the goal post works, or rather can work. It is aggressive Gerrymandering, allocating senators by state and not population and the electoral college that screw it up in the US.
Multiple parties makes gaming elections much harder for moneyed interests.
For the vast majority of it's existence, the 5th republic has had proportional representation in the legislature (only changed with Sarkozy, who instituted 2-round elections - IIRC).
Presidential has been 2-round for much longer, perhaps from the beginning of the 5th republic.
Straight FPTP as implemented in many places in the US allows plurality winners (ie, winners that don't get 50% of the votes), France's system does not.
Uh, no. The Fifth has has two round legislative elections since its beginning. The entire reason for it was that the Fourth and Third showed what an overly powerful parliament caused, as well as the relative instability of having only a single round to elect députés.
Hence, the Fifth was started by a former general who thought that putting immense amounts of power in the president was a good idea. Because clearly counter powers are overrated.
Additionally, french legislative elections can have a very peculiar situation where the second round has three candidates, but that requires a specific amount of votes and to all be extremely close. I believe there's 10 of them planned this year according to polls, over 577 circonscriptions.
Regarding the 3 candidates in 2nd round - yes that's only possible because France allows 3 & 4 candidates to go into 2nd round if they have over 12.5%. This is usually not the case, so 3-rounds are very limited but as you indicate they do present a plurality win possibility.
[1] https://en.wikipedia.org/wiki/1986_French_legislative_electi...
Hilarious to read that as the US presidential elections take over a week to tally results, when french elections have 90% of the results at 10PM on the same evening (most voting places close at 7PM)
If electronic fraud is a concern, we should mitigate it, because encryption, identity, and date integrity are solved problems.
Furthermore, spot auditing and paper receipts/copies are a thing, or could be.
(Also, voting may be "solved" but voting systems and universal access to the ballot has not. First past the post voting is possibly the worst system to use short of flipping a coin.)