It's in beta. It's missing classes and content. It's not going to keep people's interests indefinitely. They just need to make it a great game and ramp up the hype machine before it goes live. It doesn't matter how popular a beta is. Betas should be for testing.
These days there is virtually no difference between open beta and a release, if the game does poorly in beta, there is little hope it will improve during launch. The core 1-45 experience is set, while its not bad its certainly not new or refreshing in any way.
The 1-45 experience was intended as a beta and not meant to hold people for the long run since most of the end-game systems are not present. This update is bringing the endgame systems and full launch content + any gameplay adjustments to get the game to launch level.
The game has had over 50 patches, whatever your friends experienced has likely been altered and there are also going to be changes to the 1-45 content along with the 46-60 content added (if they continue the pattern seen in previous patches.) No accounting for personal taste, if you don't like Bless, then there is another MMO for you, the questing system is exactly what attracted me to Bless in the first place (this being someone who has levelled multiple alts in FFXIV, WoW, and Aion).
This proves my point, Tree of Savior is the 24th most played game on Steam, 3rd most played MMO (after Warframe and Riders of Icarus, that's a fantastic number! Likewise Wildstar as you noted earlier is the 138th most played game on all of Steam, and that places them in the top 10 MMOs on Steam depending on the time of day. Also, Tree of Savior is not a steam exclusive (same with Wildstar) and the majority of ToS's playerbase is in Southeast Asia. 9k concurrent players is amazing for any game.