I find the Vietnam era assessment to be extremely doubtful.
China has had access to decent Russian ESM gear for over a decade now, and every time there is a report about PLA exercises, there is a strong emphasis on the units ability to operate under electronic warfare conditions.
Based on China's electronics industry capabilities as well as the level all their other electronics gear seem to be at, it would need almost a concerted intentional effort to stall their own progress for their electronic warfare capabilities to be only at vietnam era level.
The key elements are will and capability. The PLA clear recognizes the importance of electronic warfare and also have the technical capability and financial and human resources to develop such technologies so there is no reason why they would be lagging so badly in this field compared to the progress they have been able to achieve in all others over the years.