A build with very good AoE damage is required for the Pit. Maybe OP’s build is not the right build for the Hordes.
Another point to consider is the damage the build is able to do because also Elites and Bosses have to be killed very fast. Being comfortable in T4 is not enough. I would recommend to have a build able to at least clear Pit 75 to be efficient in T4 IH.
I am currently playing Heartseeker Rogue in T4 without any problem. I cleared up to Pit 65. Above, it starts becoming difficult. The build is good and it will get better. Currently, I have no problem getting >1K Aether in T3. Don’t even need a 10 wave Compass. But, if I move to T4, I can’t get yet the 666 Aether to face Bartuc.
Unlocking T4 and playing in T4 are too completely different things. While most builds can do do the first, many are still too weak for the second.