I agree to everything. Except the notion massive damage is "broken". It is clearly working as intended.
Does that mean I think it's necessary or that you're bad for wanting to dismiss it? Not at all. Does that mean I think it is wise to have a level+2 enemy in a quick intro adventure (I believe Paizo released a free 4-hour scenario featuring a L3 Ogre)? No, I think it is a mistake to expose potential customers to random loss like that. As the first stage of an adventure path, sure. As a one-off especially made to lure in newbs? Daft.
The grognard in me made the argument it's needed for level 1 characters to suddenly die at all, but hopefully you saw the smiley. As a PF2 GM I definitely don't need no extra help in killing of my characters
As for "it's not clear", I believe it is very clear. It's there because the game has had a massive death rule way back. So, yes, it's a vestigial system.
Instead,
I believe it's there because Paizo concluded they would get more flak if they removed it than if they left it there. Remember - if it wasn't there, people would have made complaints based on their own fanciful version of the rule, rather than what Paizo actually ended up putting in the book.
Since you're the only one complaining about having it AFAIK, I think Paizo made the right call
Most people will just shrug, especially since as you say it ceases to be an issue already at level 2-3.