You see, I personally, want to be convinced that there are real musicians, playing real instruments, in my living room. That, after all, is what a mastering engineer is usually trying to maximise.
The ideal bass roll off of the loudspeaker will be decided by the room - I guess that's why ATC offer the three models with various bottom ends. What they can say is that it's a loudspeaker that many a mastering engineer, will have used as his or her mains/midfields.
He or she is mastering for domestic acoustics. They are assuming that the results they get will more closely resemble those that the listener will enjoy. I think it's presumptuous at best to try to second guess the engineer by removing room interaction. That is not something the engineer would have envisaged.
The acoustic of my living room is familiar to me - I certainly think that and I want the music to sound as if it is in the same acoustic/room as I am (this may be different with orchestral works). I find with that, I get such accurate timbre that I am often forced to look up or look around as I am convinced there is an acoustic guitar or a snare drum in the living room. That is what I aim for. That is very different to what a recording engineer is.
They want to hear the level of each track that they are mixing. They have no domestic settings in the recording studio or the recording booth. They want to hear everything in the right space and time. It is later that another engineer, in a very different acoustic, add realistic tonality IMHO and it is THAT which is important to me - not being placed in a fairly dull sounding recording studio (again different for a classical music lover). That tonality is natural to the room. It is natural when I speak to friends sat next to me on the sofa.
Those are my aims and, as I say, they are personal and I do not listen to orchestral music. Each to their own. There is no right or wrong path there - it depends on the listener's personal goals, and which design gives them the most musical pleasure with familiar tracks over a period of time.