Neither of those headphones are particularly flat, and both are much different than what most consumers use to listen to music. The reality is that a $100 pair of MDR-V6's (or another flat headphone in that range) will do the same/better job at getting the right mix.

Another reality is that speakers are better. I agree that those focals don't go low enough (55Hz), but that doesn't mean all speakers have that problem. For the ~$1,700 you're looking at dropping on headphones, you could get a very good setup for production. This is, of course, if you have the space & necessary acoustic treatments for it.

If you want a high-end pair of headphones, just get the pair you enjoy most. But neither of these are popular among engineers. You can still do a good job, but you have to know what's different about them and adjust accordingly. It's just less convenient.

If I had to choose one, LCD-X. Super uncomfortable, though.