Keep in mind, you are basing your opinions off of very limited information… it is 2 seasons away.
1: They have mentioned things along the lines of Mantling being added (Grabbing the edge of something and pulling yourself up) to the game, like being able to hang off the side of a ship.
2: In the same announcement they did say they were adding deployable traps to the game
3: From what we can gather, the Harpoon Gun will take up a weapon slot, and it doesn’t do any damage. So any boarder using this will be handicapped to 1 weapon till they get to the Weapons Chest. Who knows, they could add some mechanic that would make accessing another ships Ammo Chest or Armory harder for other players (Like have it take a couple seconds to access like stealing the maps off the Quest Table, have a similar function to opening another crews Armory) which would make this even more of a challenge for the boarder.
4: Based off of other things in the game, the Grapple Gun will have a unique sounding shot, and will undoubtedly have a unique sound for the impact of the harpoon, and the reeling in as well… so any boarders using it will be well telegraphed.
If you didn’t know, Sea of Thieves also has an insider program, which they ask the community to test new weapons/items/events/features for future releases. You can sign up for it on the Community Tab under “Get Involved” and when they eventually do test upcoming features they do ask for players feedback on them. You just aren’t supposed to talk about the stuff they are testing on the public forums.
While it is common in the video game community, reacting to only partial info doesn’t do anyone any good, so don’t jump to conclusions that the Harpoon Gun will be a death-knell to the game till we have all the other things that are going to interact with it.