It's why we always do rightsizing and never numerical estimates. You can calculate delivery dates by counting stories * average story time - very fast, very simple, and amusingly at least as accurate as detailed time estimates. Has an interesting side effect of tying scope to delivery. So if you want to reduce delivery time, it's clearly understood as under control of stakeholders and done by dropping stories. If you can't rightsize to a reasonably narrow range (we use 1-5 days) and have to estimate (e.g. sifting stories for prioritisation purposes), t-shirt sizing usually works ok and gives the required info without opening it to abuse.