I'm sorry that you were injured. There are two things I'd like to point out. First, the TBI injury which you describe is actually very rare. I suspect that there is a similar percentage of TBI injuries from walking down stairs. Head injuries suck. In fact, you mention Boxers and hand fractures, but the larger concern, imo, is Dementia Pugilistica which most link directly to TBI from repeatedly getting punched in the head over a period of time.
Second, while I cannot speak to your injury or your Sensei, it is common for Judo clubs to focus so heavily on the competition (Shiai) that they turn training sessions from Randori into Shiai, where instead of training and learning, the participants feel they have to "win" and go full out. Many Judoka predicted this as a consequence of Judo being included in the Olympics. They believed, and it has been born out, that this would encourage Dojos to stop teaching the old methods and focus on Shiai to the exclusion of all else, and it would lead to cumulative injuries. Judging by the number of old Senseis who now have teach from the side of the tatami because their bodies don't work right any more (particularly knee injuries), I'd have to say it's true. In fact, Kano warned about the dangers of focusing too much on competition. But the allure of the Olympics, and how it would promote and elevate Judo, was too great.
If you want to rejoin Judo, and I truly hope you do, find a Dojo which does not focus only on competition (avoid College clubs, ime). There are still some which have light or restricted randori. Be sure to let the instructors know about your injuries and your concerns.
FWIW, this phenomenon is not restricted to Judo by any stretch. I have some training buddies who also do BJJ, and they're beat up pretty bad too. Spinal injuries are becoming more common.
Peace favor your sword,
Kirk