Why endurance change to something that was never on any live server?

There will always be a speed standard. Removing the ease of permasprint speed 6 will simply skew fights in favor of groups that prioritize it, returning us to an unequal playing field. The freedom to engage and disengage will no longer be universal, it will be decided by dedicated 8v8 groups who have all invested in potions and the appropriate Long Wind level for their class. LW2 for casters, LW3+ for melee. Anyone who wants to match them without being run down like dogs will have to consider if everyone in their group is able to permasprint. This became a nonissue due to its cheapness paired with potions, but now it isn't. You'd better have a bard on endo song duty, enough conc on your shaman, or by some blessing of luck, an actual paladin in Albion. The only class among those three that lacked appeal in groups was the paladin, whose utility could have been further buffed in some other way that didn't upturn a major QoL feature on the server.

This change is a significant nerf to melees who will struggle to stick onto targets, an incentive to favor caster compositions that only need LW2, and a death blow to small man and casual pickup group viability. Players will adapt, because we know how this works from Uthgard and live, but the effects are disproportionate and in my view diminish RvR balance and overall appeal. Expect more sitting around waiting for the right class, and disregarding other classes because they no longer fit your narrower required composition.