The thing is, they have a system for closed testing. First is the bug testing, in which they use a system similar to the new training system that runs automatically. This system runs literally hundreds of thousands of bug testing every day.
Second, the internal play testing. This is where they have Rioters and gamers play test new things in sort of a closed alpha state. I'm fairly certain that they primarily use this for new additions, for example, new items or champions.
And then obviously the PBE.
However, none of these come close to what a single hour on live can do. First off, in all of their testing, typically the thing is being used as intended, by who it's intended to be used. Not as much on the PBE, but things that are determined to be too strong/weak on the PBE often turn out to not be so when they're officially released. Remember when every YouTuber who played her declared PBE Taliyah to be busted, and then, with no changes to her at all between PBE and live, she released with an absurdly low win rate of 30%? Why did she feel so much stronger in the PBE testing? Well, part of it can likely be attributed to the skill difference in the players, as well as the fact that there is a single, globally accessed PBE server, meaning people in continents other than NA will have much higher ping than usual. The other thing is how certain champions seem so broken to lower ELO players, Master Yi being probably the single best example of this, but once you get to higher rating, he's nonexistent because of how easy he is to stop. He's squishy and relies on dealing sustained damage in melee range. Literally all you have to do is focus him when he dives in and he gets completely ruined. Now imagine you're a Korean professional player, and you're playing on the PBE server. In your game, your team consists of people whose accounts on their real servers are anywhere on the ladder. You could literally be a pro playing with bronze on the PBE because it doesn't have as many players or as sophisticated of a search system. Because of this, any feedback as to how good something that's on the PBE is has to be taken with a grain of salt - literally, depending on how salty the player gets. It could be he just doesn't know how to play with/against it properly.
