The heroes have been picked as the best performing ones from the Divine and Immortal brackets.
The choice of heroes has been made from a combination of high pick rate and high win rate heroes.
The second impactful spell, of course, is Aphotic Shield, which has been buffed in recent times.

In Dota 2 patch 7.34e, the barrier capacity of Aphotic Shild received a buff.
In patch 7.35, he got a new talent at level 10 which gives Aphotic Shield +15 HP regeneration.
That is a huge buff for the support Abaddon.
Had this talent been at level 15, its impact would have been significantly lower.
In addition to all this, Abaddon is one the best carriers of Solar Crest.
But times have changed.
In a meta where magic damage is strong, that is a strong skill to possess.
That was obviously broken, and was rightly rectified.