Joey the king of DIY is very well known and respected. I'm not sure how he was presenting the video you mentioned but I would be surprised if he is recommending six full grown Oscars in a 6-foot tank. If you're not sure, then I suggest that you might post your question in the video comments. See what his response is.
He does address long term when he moved them back into the 180 and that's part of what ultimately turned me off because he comments that he suspects they will eventually form a pair and he'd have to move the others out. I don't want to do that. But he repeatedly says he loves and greatly prefers how they act as a group compared to individuals or pairs. He says "I'll never keep oscars alone again". Still not saying he's right, just point of discussion.