Mixed martial arts is good if you have a very strong base on one martial art system. After you have mastered the base art, you can then blend other martial arts techniques over it, however if you do not have a clear understanding of each system of martial arts then it is as good as mixing tea coffee cola in one beverage.
Hence for a MMA aspirant It is essential to have a strong base in one system and then gradually add other systems and techniques. Mastering your base martial arts will help you operate techniques efficiently while using it during combat.
It is beneficial to know other systems too, as all systems have benefits and advantages . In learning the art of war you need to have your own specialization. Quoting Bruce Lee who said I fear not the man who has practiced 10,000 kicks once, but I fear the man who has practiced one kick 10,000 times If you do not have your own martial arts specialization you will be like a jack of all trades, not knowing any one martial art meticulously. When you train mixed martial arts, blend it but also learn other systems, spend time to do those systems and do not limit it to just a few tricks of the trade. As per me Mixed Martial arts is being able to combine the various ranges – long range, medium range, close range, grappling and going down to the ground. A mature fighter needs to have an understanding of all ranges and different martial arts operate in different ranges! Pick and choose a martial arts which is good for that range and go ahead and train MMA for survival.