Way more arguments on Lemmy seem to end with the two users stop down voting each other, and then basically concluding 'that I see your point but still think you're wrong because youre over emphasizing x or y'.
Way more arguments on Reddit just end with an endless loop of insulting and talking past each other.
I think the effect is probably like 30% selection bias of people coming to Lemmy more intentionally, and 70% lack of bots. Between paid influence campaigns, and Reddit's own use of bots to juice engagement, my gut feel is that most of those endless arguments are either directly arguments with bots, or indirectly people who have grown so frustrated arguing with bots in other threads that they're no longer capable of rational discussion.
Also, Reddit comment quality has nosedived in the past year or so. Like, wildly nosedived. It used to be that there would be at least one comment in the top comments that adds some more interesting context to the story, these days, I almost t never see that on Reddit, but frequently do on Lemmy.
You can also really feel that the algorithm doesn't just blindly promote click/rage bait the way that reddit's does.
It still gets promoted some times, but the front page isn't constantly filled with it like Reddit's is,.