Stereo image is another big difference. I find with open backs you get a more natural stereo image than the extremes of closed back.
And the experience when tracking comes down to the space a LOT. One of the nice things about open back is if you’re tracking with other musicians you can hear their audible cues without talkback mics, and you can be more natural in the studio. And the 990’s don’t bleed badly if you’re using directional microphones. BUT! you’re right, some people really prefer tracking with closed backs (or need to, because they’re using wide angle or omni mics or because they’re tracking vocals and need the zone, etc.) So while I wouldn’t simplify it quite so much, it’s definitely the biggest reason to go closed vs. open.
Since I don’t have live mics in my studio, I use open backs whenever I can so I can stay “present” in the space while working. But my B cans are the 770’s and I use them for guest artists who are used to closed backs, or when I want to go bumble off and jam to something in a corner while others are using the main system, etc.
As for mixing with headphones, having a wide variety of references is essential. But I remain adamant that you can definitely get a good mix (professional, proper, however you define good) with open-back headphones as your main reference provided a) you get to know them and how they translate and b) you do the usual mix engineer duties of checking your mix frequently on other sources. But that applies to monitors as well (the NS10s and auratones are notoriously less accurate than a good set of headphones today, and many amazing mixes were made on them) and many country chart-toppers were primarily mixed in mono from a single speaker! So, what you mix on almost doesn’t matter as long as it can tell you enough of the truth and you’ve adapted your ears and mixing sense to whatever bits of the truth it’s not telling you. 