Well, them joining the hero academy isn’t really exciting as with all those heroes there now + the small 5% weekly the chance to get one you are after (or even one you don’t have) will be astronomical.
Also, being a part of a joint event also isn’t really good news; if you are after i.e. Gazelle, chances of getting her were 0.2%… now with 5 events combined into single portal, that’s 0.04% - 1 in 2500 pulls.
If that joined portal isn’t well designed with odds/featured heroes/player’s choice etc. it’s going to be as bad as original ToL if not worse.
But at least we know now what the Challenge Festival is 
One less thing to distract us from planned summons…