I was tempted just now to write a long dissertation of what progression actually is and how every game since the existence of video games uses the term progression... and offers progression mechanics to enhance the game.
... and then how cosmetics are used in other games and never referred to as a progression mechanic.
it will likely fall on deaf ears however, so I will pass.
When I meet a pirate out on the seas I have no idea if he has purchased 8 different sail types, or 1....AND of the 1 sail I can see, it only tells me that 1 of the potential 4 crew members even unlocked it.... Unless, after the far to common "talk first shoot later" PVP mentality, in which instead of fighting - he insists I follow him to an outpost- I will then politely sit on the dock in waiting anticipation as I watch him and the rest of his crew cycle through the countless different skins they have each grinded 300 hours+ to get, and then I will meaningfully admit that they have indeed spent far more time in the game then I have. But have progressed nowhere.
In fact to prove the point I will present the following arguement:
If Rare dropped all cosmetic purchase requirements and offered a Detailed customization center. (colors, decals, etc. etc..) so from the very beginning - all pirates/ships could be unique and had diverse options to make themselves whatever they want. This game would probably have more players right now than it does. as lots of people who have left, became bored. And many many players don't have 25+ hours to grind for a single type of sail, that probably isn't even exactly what they want anyways.
which concludes that if all forms of the current "progression" system were removed and made accessible to everyone that the game would have more players. And what game becomes more successful when all progression is removed?