Sounds like pure jealousy to me. It's not like we are on a pvp-server where the strongest rule the world.
Well, 10 years ago, people were considered "powerleveling" by groupkilling huge mobspawns. So, nowadays we do not have any huge mobspawns of this kind anymore. HZ has been reduced to a grinding festival.
And btw, you do not gain any xp anymore, if you are in a "safe spot" - like sitting on a tree or on a wall. Does this improve HZ-gameplay in any way? Nope. This doesn't fix any bugs nor does it improve gameplay. But it took up developer-ressources to get it programmed, time that could have been used to fix real bugs or other issues.
I'm glad that my Dwarf has already his important adv schools at 100, because right now, leveling is an impertinence. And thats no matter whether I look at any of the remaining schools of my multi-lvl100-Dwarf or at one of my other lowlevel -no-lvl100-chars. The current xp-gaining system is more likely to keep players away then keeping them ingame
Oh, and group xp? well, at least on order hardly anything to talk about, because - which groups?