Virtually every single MMO I have played has a PTR build and it significantly reduces major bugs. The ones that do exist tend to get hotfixed within the first week or so. This also gives players valuable insight on mechanics and what will be good without having to rely on Streamers to parse all the hidden mechanics and do the not-so-fun testing during the Live Release, allowing you the player to focus on…playing.
For this being a Live Service game, it feels really behind. I mean, we had Malignant Hearts that were obviously broken that did not even get fixed until what, less than a month left in the Season? There are still some that are not working correctly and have bugged interactions (Berserk Ripping and Barber lol). This would and should have been caught within maybe an hour of testing. It is pathetic.