Shia Pakistanis can be from any ethnicity. We have 5 main ethnicities in Pakistan. Punjabi, Pashtun, Baluch, Sindhi, and Kashmiris(although Kashmiri is a broad term, there are many different ethnicities among Kashmiris). There are Shias among all of them. Surprisingly, the Pakistanis that have descendents from Iran usually have last names such as Hamdani, Isphani, Shirazi, and most of them are either Sufi or Sunni.
So although they are from different sects, they are still more or less from the same race.
Agha Khanis or Ismailis, especially from Gilgit Baltistan are very good looking people, closer to Iranians, but they do not look like Turko-Persian whites from Tehran. Also Tajiks which are Sunni and fall under Kashmir umbrella, have more resemblance to Iranians/Central Asia then others. Shia Muslims in Pakistan may not be better looking than Sunnis, but many of them have lighter skin color overall, although there are exceptions, which leads me to believe they might have had ancestors from Iran or Afghanistan.
The people of Pakistan are very complex. There are so many races, sects, and people that even we are usually confused. Pakistan is truly a melting pot of different people and cultures.