The post seems to implicitly assume that groups are better for Reasons. I just want to explicate on why that might be the case:
Additional ideas / new perspectives: typical mind fallacy is prevalent and gaining more opportunities to see how others operate can be helpful. Also, you might find novel solutions to your own problems.
General benefits from socializing. Pretty sure that problems from social isolation are fairly well-documented.
Precommit to doing things: positive peer pressure + social bonds mean you might feel more compelled to make progress.
Additional help / support: it can be good to have others you can rely / lean on when you are in a tough spot. Gather allies and make new friends!
LW has a problem. Openly or covertly, many posts here promote the idea that a rational person ought to be able to self-improve on their own. Some of it comes from Eliezer's refusal to attend college (and Luke dropping out of his bachelors, etc). Some of it comes from our concept of rationality, that all agents can be approximated as perfect utility maximizers with a bunch of nonessential bugs. Some of it is due to our psychological makeup and introversion. Some of it comes from trying to tackle hard problems that aren't well understood anywhere else. And some of it is just the plain old meme of heroism and forging your own way.