With Gyms you must have more than 1 if it is 3 on 3 (or more). I would guess the same rule applies. If they did allow Takuto to enter with just 1 then it would be unfair. Think about it, if people were allowed to enter with only 1 or 2 then their opponents would have less pokemon to defeat while others have to go through 3 , 4, or 6. Even if they were really strong, it still isn't fair to everyone. But you're right, we don't know completely, but I would guess that it does apply.