To be fair, it depends on what you call a digital monster. The term was originally not just for groups that constantly put out smash title tracks. Acts like Sistar, 2ne1, IU, Big Bang were called that because even their b-sides would storm the charts.
Later, people started to use it for acts that consistently did well with title tracks. So among the ones discussed in here, only TWICE was ever really considered digital monsters in the latter sense.
Yes true. In the old days, only those acts that can line up their album songs on top of the charts are being called so
The terms have been used so loosely nowadays to refer to those that only do well with title track