'Spawn camping', IMO, is just another way to say 'overextending'. It sounds like the perfect strategy, if they can't even leave spawn then they can't win, right? But going all the way up to their spawn and being as aggressive as possible about it is an unnecessarily risky way to accomplish this. It's not that hard for them to slip past you, and once they do it was all for naught.
That video was hard to watch, seeing Green play so stupid. It's like they just kept forgetting the Roller was there, and didn't take advantage of the fact that they have a wide open area to fight her from, letting themselves get ambushed right in the open where that shouldn't be happening.
Now, the idea of just trying to ensure the opposing team can't advance is a central tenet in shooters, but to do it effectively you have to be a little smarter about it. Namely, you have to pick where you want to block them, and usually the correct answer to that is not "right on top of spawn". The correct answer is at a choke point, a tight space that's easy to guard and hard to slip through. Let me use Walleye Warehouse, one of the chokiest maps I've ever seen, to illustrate this:
From Blue's perspective (rotate 180 for Yellow), they should just focus on making sure the opposing team can't advance past these highlighted circles. The two narrow tunnels are easy to lock down because they're so narrow, while the central entrance is easy pickings for a Charger standing on the center crate. By giving the opposing team a little breathing room behind these chokes, you can much more easily pick them off at the chokes. It's a far safer way to lock them down. It's alright to back up and let them have the area behind the chokes, because you're still denying them more than 50% of the map. And that's all you need. If more than 50% of the map is yours, you win!