Here in NL, large festivals have drug testing booths, where the visitors can have their drugs tested so they know what they'll be ingesting. That's possible because of decriminalisation and destigmatization.
Legalization would allow the government to create a testing infrastructure so drugs can be tested/validated before they're sold, that's arguably better. But it's definitely possible to create a safer drug environment with decriminalisation only.
Drug testing is possible here in the US with overt criminalization.
Decriminalization is just marginally safer. Testing is a huge waste of resources unless its a stopgap towards recreational legalization with a reliable supply chain.
Legalization would allow the government to create a testing infrastructure so drugs can be tested/validated before they're sold, that's arguably better. But it's definitely possible to create a safer drug environment with decriminalisation only.