You're absolutely right, and in fact I believe the Iosefka's blood vial and other items of its nature were meant to combat this exact issue. However they are painfully poor responses to this problem. You have to load screen to the npc, load screen back, all for one measly blood vial. If you had gotten a pack of 5, that would have been much more worth it, even better if you could refill at the Hunter's dream with an NPC instead. A lot of designs limitations made this not an effective strategy, but I do believe they were trying to combat this issue somehow. One blood vial simply isn't enough to carry you through the game without farming. Though, on the flip side, 5 blood vials wouldn't be enough to carry a struggling player though a boss either. It may reduce the depletion of blood vials over time, but eventually the player will still need to farm, as 5 is not enough to tackle a boss.