The biggest problem I had with JJJ and most other 'traditional' martial arts is that they seem so dogmatic.
The beauty of mixed martial arts is that it innovates and isnt afraid to change and develop, people go away and cross train in other disciplines then come back and incorperate those techniques into their MMA. You dont really get that with alot of more traditional martial arts.
Another think I dislike about traditional martial arts is that theyre so expensive. It costs a fortune to do your gradings, you need loads of equipment and at the higher levels in things like JJJ you need to start investing in silly stuff like swords and what not. With MMA I need my subscription fee, my gloves, my gum shield and a pair of shorts - simples.
Its true to say that any martial art is better than none - for adrenaline conditioning more than anything else - but I see little point in spending a fortune to do something like JJJ when there are more effective disciplines out there that wont break the bank. Martial arts has developed more in the past 15 years than it did in the previous 500 and MMA is the future.