First of all, problem with fentanyl is that it's ~100x more potent than morphine, or ~20x times more potent than heroin. While many people read this as "it's got 100x times stronger high", it doesn't mean that (actually it has shorter acting high, more adverse side effects and slightly less enjoyable high compared to heroin). It's just means you need 20x times lower quantity for comparable effect. Given that into account, you need 20x lower quantity to smuggle. It's physically impossible for ANY agency to control millions and millions of postal shipments containing small amounts of contraband. It's one thing to push 100kg containers of heroin, and whole another game ordering 50 grams from Dark web. It's incontrollable in that way.

Second, what you're basically asking for is MORE WAR ON DRUGS. Addiction is public and mental health problem, and should be approached as such. DEA is the last agency you should plead for help in times of crisis such as this opioid one. Harm reduction programs are proven as best way to tackle such problems, proven time and time again around the world.

Third, calling fentanyl "Chinese fentanyl" is reminiscent of recent declarations of "Chinese virus". It's fentanyl. It doesn't have nationality.