So you are saying that everything except narrow/medium grip bench pressing is inefficient or even worthless for getting stronger? If you widen out your grip in the bench, what happens? Your bench stroke gets smaller, and (if you are like me) you bench less weight.
Why not just go do some reverse band work off of a giant camber bar? Since the bench press in equivalent is a "little movement with little weight".
Alright, so we just figured this out: Reverse band work off of an increase range of motion is superior to everything else. Great, now let's throw eight strong reverse bands on, and not touch with less than 600 pounds and we'll have the best most effective exercise every!!!111!! Do you realize how fucking stupid your statement was?
Okay, so here is the purpose of the floor press: To slightly reduce the range of motion (it only cuts the bar path down by a 1-2 inches maximum of my arched bench) while separating the eccentric and concentric allowing you to reduce the stretch reflex, and essentially do the upper body equivalent of a deadlift. That means to lift the weight you are forced to press as hard and quickly as possible making you generate more force (and likely increasing your capability to do so), while strengthening the mid and top range of the bench press and even the bottom range of motion (there is a 15 joint degree transfer of strength). It also removes the ability to have leg drive which also contributes to why you use less weight.
I'd definitely say that the floor press is equally effective as the bench for building strength, and possibly more effective to the bench for certain things.