Just a thought ...
Mount speed all the same during the event.
Or faster or slower.

Also i hope that high levels will stop killing the boss before slow pokes can come there for now.
You will get the achievement any way but you can be a very big help for ya fella Rifters .

I missed a dozen bosses just because my mount can't get me there in time because high levels are not only faster they hit much harder so the boss dies much faster than he should

This way we could all be more happy and have equal fun .

(befor the Grammer Gestapo is trying to bust me English is not my native languages )