The remaining population of COVID patients is a good control group. Or, if you prefer, randomly select sub-populations with similar demographic statistics.
Compare 700 people who received a treatment to 700 demographically similar people who received the standard treatment in the same or similar hospital and you're going to get a useful result.
We can do your fancy RCT later when we aren't dying en masse from a novel and highly lethal virus.
In the end we will most likely find that all positive anecdotal evidence found was just confirmation bias. That's why RCTs are so important.