Check out these 2 games for a ridiculously dominant invoker. Iceiceice going ham on everyone.
Zenith vs coL game 2
Zenith vs coL game 3
I think an Invoker has a different role compared to a magnus/qop/ss. He begins to strengthen other lanes at level 2 if he's going exort. He has great AOE damage, disables and even pushing ability. His forge spirits can constantly scout like in the 2 games above which is invaluable.
The problem is he's so damn hard to play at his maximum potential. I am sure he will still be a top pick in the International 3 for teams who can play him well. I won't be surprised if some teams play a Magnus offlane and an Invoker mid.
He's definitely among the hardest heroes to play at maximum potential imo along with Chen, Tinker, Meepo etc. Just don't use key binds because that's cheating.