It was that way in the old days. Today's modern dual SIM phones are fine. The OnePlus3 handles text on both, voice on both and data on one that you can switch back and forth.

It is also tolerant of different network types. The OnePlus2 had issues when one of the networks did not have 2G support. Seeing that many companies are turning off 2G to use the frequencies for other products, this is becoming common in the more developed world.