The thing about LoL there is no testing done ever. Look at all of these champions on the PBE to be tested by players and then look at them on Launch. These champions are on PBE for about a week or 2 depending on the what they plan to release in the patches. Some of them are so under powered that it's beyond stupid to even have it on launch. Or we can go with the overpowered that it has it's own reserve on the perma ban list until it's gutted.
No I'm 100% sure PBE is only there to create hype when Streamers/Youtubers display the new items/champions/game modes.