@corentin-1236 You've probably heard or seen other players take on galleons with sloops.
Sloops have a really huge advantage to galleons. Now if you are solo than all I can say is learn how to run away properly. You can fight against a galleon solo, but unless the conditions are optimal than its probably a death sentence. If you are a 2 man crew than what I suggest is fighting it out. If you are having problems with defending yourself. I suggest finding someone you play with and get on a sloop and then go out into the world and hunt down galleons for experience.
My teammate and I go out hunting for galleons in 2 man sloops ALL THE TIME. Its about experience and knowing what to do. Even with one chasing after us, we sink them and go about our day.
Ask, read, learn, try. Gain experience. Instead of saying "this is impossible" reflect on what happen and what you could have done better. If other people are doing it just fine than the server is balanced and honestly just means you need to get better. Sorry but its true.
Thank you for your time.