Here's a bit of an academic view from a professional musician and studio owner who tracks/mixes/masters many clients. My belief is that you cannot understand this topic completely just thinking about the speaker and room alone. I'll make a few truisms and see if people agree.
1) Flat Response speakers with accurate phase in a decent room properly communicate what the microphone is picking up when you're tracking.
2) The ideal speaker to mix on is the speaker the end user will listen on. And by the way, it won't be the speaker above. If you make your mix satisfy you on speaker X, then with a similar room, it will likely satisfy (approximately) the end listener.
3) End listeners do not listen on razor flat speakers with accurate phase (by the way that also means no ports). And I believe that historically, a typical end user speaker didn't have excellent high end and thus were a bit muddy.
OK. What does this all mean? My experience is that when I mix on my Dunlavy Mk-VI speakers which are razor flat or Genelec, in the control room, it sounds just like the mics and the mix sounds incredible. Then when I play back in the car or elsewhere, it's muddy.
My conclusion is that the accurate studio speakers help you to here exactly what you recorded but......you need to adjust you mix by listening and evaluating on muddier speakers. Then, your mix will sound right there (and too bright on your Dunlavy's).
I think it's a historical problem. If audio began for consumers with flat speakers, we wouldn't be having this conversation. Historically, engineers mixed bright for the average expected consumer speaker. Then we had to continue forever. I mentioned this to Bob Hodas (who tuned the rooms at Abbey Road) and he replied with "You've learned a powerful lesson on room tuning".
I'm scared to hear the response to my dissertation. Thanks, Anthony