When we talk about Balochistan then we should be clear that we are talking about geography or ethnicity. What I understand from statement is ethnicity. Quetta is historically Pushtoon dominated city and Hazara is second major ethenic composition. Naturally the gathering has to be Pushtoon and Hazara dominated. If I remember correctly Mujahid Bralvi was covering the gathering for CNBC channel and while moving towards stadium, he kept asking people about places they came from. Many people were from Quetta itself , pishin, chaman, Zhob, sibi etc. There were People from Baloch tribes too.
Considering your statement if Baloch tribes had less or no representation then any ther party which can gather them, may it be PPP, PML (N), JUI, MQM or any one else must come forward and do that, am sure that party or leader will be equally appreciated as PTI is being appreciated.