All I see on this forum are users who stan two, three... groups from the same company and it's "normal". Well, I agree that it really is N-O-R-M-A-L and there is absolutely nothing to argue about it. So why do the views change drastically when it comes to Hybe/Bighit? What's so problematic about it?
Fans move between groups from the same company since the beginning of Kpop. There are a lot of people who simply like music and are open to getting attached to artists who captivate or please them.
I can see that the so-called "big 3 privilege" exists and it extends to Hybe/Bighit nowadays. Debuting under these 4 companies gives groups great exposure that may resonate on an early fanbase but it's up to the group themselves to grow their audience. This is the reason why some groups take some time to become successful and others don't. For some reasons (mainly sonically or aesthetic factors) they fail to connect with fans of the previous groups and need to conquer a new audience.
So TXT and Enhypen aren't successful because of BTS, they're successful because they captivated an audience that was open to them. They're not reinventing the wheel, they're just serving what the public wants from them.