The only reason the last 2 raid series felt HP spongey was because as per Yoshi-P's own admission, alliance are designed so a few players can carry the lot. The main downside of that is when not enough people contribute, the bosses take too long to die. They probably undertuned the HP for the current raid bosses to mitigate that. As it turns out their mechanics are also really simple this time round, so it's really noticeable how fast they get killed now.