If it’s Melenchon then things will be unpredictable as it’ll come down to who the centrists vote for - and there are plenty on the right who would never vote for Melenchon. However if shes against a centrist, then she’s more likely to lose even if they’re deeply unpopular now, because they’re the easier “anyone but Le Pen”.

Where is the evidence of this? This assumption proved catastrophic in US elections, Biden was an awful choice to run against Trump and so was Harris.