Guild Wars 2

First its not entirely just pugs jumping in the event too late, but its the fact that if you just joined in solo you were thrown into an overflow with fewer people.

The way it works is that all maps including overflows have cut offs to how many players can be put in. The way to bypass this is to get partied with someone and join their overflow. What this means is that the maps that actually has a chance to defeat him are completely maxed out with not the 70 players randomly put in an overflow but at least 130+ players cramped in through manually joining it. So anyone joining in a few minutes early will thrown into overflows with significantly less players than those with players spamming the “Join overflow/map from partied members”.

All meta bosses are scaled by the number of players but there is a limit seems to be close to the that cut off that A-Net implemented which is why when servers completely full maps can easily kill lets say Karka Queen in under 3 minutes.

TL;DR Overflows actually has fewer players than main servers make killing Teq impossible.