I will try to answer as best as I could. A voltage amplifier is just an OTA with a buffer output stage. As such, a voltage amplifier can drive resistive load. The current needed to drive the resistive load is sourcing from the ouput buffer stage such that the gain of the amplifier is not affected. On the other hand, an OTA is not suitable for driving resistive load because any current needed to drive the load will have to come from the output stage of the OTA. Subsequently, the performance of the OTA will be affected. But OTA will be suitable to drive capacitive load. Hope that clears your doubt.