Fediverse

This is being overly simplistic IMO. Lemmy is not a direct copy paste of reddit, just the idea is the same.

But he's not wrong on a practical level, the content is almost the same on reddit and here, even the memes are being reposted from there to here and then reposted over and over.
To me, seeing the same content multiple times on the All feed makes it seem emptier, like I can just check it once a day and I won't be missing anything. I blame the accounts that post content on multiple instances/communities instead of posting once and letting it federate and the reposters who just recycle content over and over... maybe those who keep blindly upvoting too.

A normal user doesn't have any incentive to leave reddit if they are going to find the same things.

If there’s something you are passionate about there’s nothing stopping you or anyone else from spinning up a community or instance about it and creating the niche communities everyone seems to miss.

Yeeeeah no, as I said on another comment, creating a new instance requires some kind of investment, might be monetary, learn a new skillset or dedicating time to keeping it up, it's not something anyone can do/afford and as time goes on, it might escalate if you plan to preserve everything.
A new community... maybe, but then you're gonna have to go instance jumping until you find one that fits you and it might be quick or you might never find one.