Is it better to focus on one hero type or try and balance with all three?

I've seen a few people just focus on one damage type and i'm wondering if that's where i'm going wrong.

I have all 3 hero type artefacts at around level 32 and sitting at MS 2000.

My current skill setup is IP @ lvl 9 and all three hero type skills @ lvl 2. Basically I've just been buying the latest hero i can afford and then swapping equips and pets to match.

Is that viable or should i focus on just one? Helm wise my Melee is my highest multiplier at x20.

Thanks in advance guys.