No, because not all rear facing seats are reclined. In fact, it's safer to be upright when rear facing as long as the child is old enough to tolerate it (it wouldn't be safe for little babies for example). It's mainly to do with keeping the head, neck and spine aligned. In a forward facing seat, the shoulders are held back by the five point harness, but nothing is restraining the head so when you have a sudden stop from travelling forwards (no matter where the impact is directed from) the head will continue to move forwards until it's stopped by the extension of the neck. That's risky in terms of the spinal cord stretching or potentially snapping entirely. It won't always happen, but it can. Adults tend to get whiplash; children, who have bigger/heavier heads in proportion to their spine and much less tolerance for spinal cord stretching (because they are physically smaller) are much more vulnerable to serious spinal cord injury.
This is why racing drivers who use five point harnesses wear a HANS device (helmet with strap attaching to the seat) to help restrict movement of the head and reduce the incidence of spinal injury and whiplash in case they crash at speed.
The other main danger to children in car accidents is head injuries. If they fly forwards out of the seat, which will always happen to some extent in FF, even if you have a very good restraint used properly, but is much more of a problem when parents install the car seat with the seatbelt too loose or buckle the child in incorrectly or have the seat harness too loose or the child takes their arms out of the straps, (and all of these are extremely common misuses making up approximately 65% of car seat use) there is a danger that they will hit their head on some part of the car, whether that is an airbag, seat in front, side door, dashboard, etc. In rear facing seats the shell of the seat "catches" the head and contains it within the shell, meaning that the child is far less likely to hit their head on something within the car. Some more upmarket models also have shock absorbing materials in the head area of the seat to help reduce any impact on the shell of the seat itself. Modern forward facing seats have these too BTW, but it will only help for side impacts/on the rebound phase of a car crash, which is the secondary impact and the effects are lesser. However, this is also why you must never use a rear facing seat in front of an airbag - those inflate with too much force and can injure a rear facing child. But even if the straps are too loose, set up wrong etc the shell of a rear facing seat will help prevent a child's head from impacting on other parts of the car, which is significant.