Vaccines have several effects. Frequently they prevent you from getting serious symptoms (or any symptoms at all) after contact with the virus. Often they reduce the time span during which you are infectious, sometimes they mean you aren’t infectious at all after contact with the virus. Sometimes (very rarely) they have no effect at all.

Only that last point can reasonably be framed as the vaccine not being perfect.

Other than that the vaccines work astonishingly well, even with delta. Them still making it possible for you to be infectious after contact with the virus doesn’t really change that.