In Lost Ark lore, we are currently just coming off of defeating Brelshaza. The only legion commander left for us to fight is Thaemine (after Akkan in KR), and after that leaves only Kazeros itself.
Currently there is no incentive to build an esther weapon, everyone at end game can comfortably fight the ‘hardest’ raids with their currently weapons, even without +25. Logically, it wouldn’t make sense that we should be able to defeat Thaemine and Kazeros with just these ‘standard’ weapons that are honed up.
Sidereals are meant to be very powerful and have fought in the chain war against the legion commanders and Kazeros, and we get given an idea of how powerful the esther weapon is during the creation cutscene. We don’t get anything like this for normal weapons.
Thus, it only makes sense that we will need a weapon imbued with their power to be able to hold our own against Thaemine and Kazeros, the strongest demons currently. Currently 33 esther materials are given for ‘free’, which already sets up players for future upgrades, meaning it should be relatively easier to get a +6 esther weapon which I believe should be the minimum for normal mode Kazeros/Thaemine, and +8 for hard mode. To balance it out, as it may be too much for all 8 players, only 1 person should need it in the entire 8 man raid, or 16 for kazeros if designed that way. They will need to use it during a core mechanic otherwise the raid is wiped.