No. I had thought there was some level of permitted intermixing and that you could have a soldier/medic hybrid of an operative/engineer hybrid. Even without that I question the design decision that defines the class system in limiting players based on characters proficiencies. It sort of shoe-horns you into playing just one thing or the other needlessly in a game that supposedly requires all classes to compete. If you have a team of all Soldier/Medic or Soldier/Operative specced characters, and need a proficient Engineer, you're SOL.
Your making no sense, just stop.
This game is about TEAMWORK, thats why there will not be a team filled with just medic or just opertives because everyone will be diffrent in order to do all the objectives and help eachother.
And if there is no one playing as one of the classes, a mission will appear to change your class to the one needed, even if you fon't have any skills in tge, lets say soldier class, and you need to blow up the objective, and no one is soldier, you can switch to soldier and do that objective, along with giving ammo.
The game is balanced.
What you are suggesting would make it imbalanced. Thus, you fail and this game is not for you.
End of story. End of topic.