I originally thought and posted that health was a useless stat since our Magimon help prevent damage from going through. This was before I studied the Battle Info and found out that Magimon with Low Turns (3-4) can get on the field fast and deal high amounts of direct damage to the enemy trainer.
I think adding health in the beginning isn't that helpful but it'll become more important starting in the level 30s and definitely more in the level 40s, 50s, etc. In other words, it's more of an endgame stat to increase chance of surviving from blows of Magimon's physical attacks. At high levels, direct Magimon physical attacks hit like trucks!
For example, I have a lineup that focus on low-turn based combat so that I can get them on the field as soon as possible. Most of the matches I win are from reducing the enemy's health to 0 and not killing their Magimon. Some people put so much effort into raising their rare 6 star Magimon although it's very possible to kill the trainer before the opponent is able to summon their 6 star Magimon.
I am currently level 58 with 130 Energy, 70 Mana, and 1320 health.
I have more than enough Energy, enough Mana to attack others and fulfill requests, and enough health that I rarely die due to being attacked directly.