Quality of gun powder in different Navies

While listening to diverse podcast in the naval months, one of the reasons of the superiority of British naval gunnery should have been the better British powder compared to the French and Spanish.

While I cannot comment on the Spanish, I cannot see anything wrong with French gun powder - assuming they used the same as the French land armies did. It was perfectly adequate to do the job. What should be so superior of the British gun powder??

Next, how was the powder stored on ships to prevent humidity ??

Lastly it is mentioned that the British guns had flintlock mechnisms and that those enabled a more calculated shot. I was under the impression that only HMS Victory had so and then again I see not that great advantage compared to the usual firing tube insterted into the vent which did ignite all of a sudden compared to lints.