Definitely a commercial failure. This drama was incredibly high budget, stellar cast, and a incredibly popular writer. A drama like this should have started with a decent rating (8%+) to begin with and steadily gained traction with some fluctuations. However it started at 10%+ and is usually getting 5-7%. Now count in the fact that it's on a free station and the ratings should definitely be higher. But people just aren't tuning in as much anymore.
I've seen the theory that it airing on netflix at the same time has tarnished it's ratings, but that simply isn't true. If you compare it to itaewon class and Crash landing on you. Like TKEM, both of these dramas aired on netflix at the same time as they did on TV. Unlike TKEM, their ratings rose despite being on paid channels.
As for if this will effect their careers:
LMH is unfortunately untouchable fans will brush this off as bad luck right out of military and people like me will weep as he keeps getting lead roles in dramas we want to watch.
KGE isn't going anywhere, if she's in a movie it's because she wanted to be as she's already done such projects before. Korea still seems to like her and I've seen a few adverts with her in them.
The writer is the only one I can think of whose reputation this would effect, in many ways she's responsible for the bulk of this mess. From cheesy dialogue beyond saving, to predictable twists and convoluted plot lines, all of those are her doing and ultimately why a drama expecting 20%+ viewership hardly broke 10%.
