The statement "Russia is a more reliable partner than the United States" was made well before the aggression, I think it's safe to say it doesn't hold today.
Do you have a more recent statement that goes the other way?
The other statement by JLM is "It is a matter of diplomacy rather than artillery fire" - I don't see how this is pro-russian.
Here in Germany those tyep of people say "Frieden schaffen ohne Waffen!", meaning making peace without weapons. It's a pro Russia narrative that undermines Ukraine's sovereignty and its right to defend itself. The conditions for making peace are already known; Russia has to stop its aggressions and return to its internationally recognized borders. This isn't even debatable, but those people who scream for diplomacy over sending weapons think it is.
LFI are hardly extremists. They're not revolutionaries, they're not communists, they're just socialists.
With pro Russia & anti EU stances I would very much categorize them as dangerous extremists. Especially with how important France is to the EU.