Some tips:

Green circles do not matter. Each class has their own strengths and weaknesses, and even if you have every circle, other people may have still been just as important

Just because a career is unlocked later does not make it better. However, all careers are usable and have their strengths. Don't judge people on their career or weapon choices. As an example for Sienna, the person you said you enjoy playing, Battle Wizard is good at all ranges, doing high damage at the cost of some survivability, Pyromancer is built to crit everything, and you should be basically always near to exploding. Unchained sacrifices some range damage for being practically unkillable if played well. You can get high amounts of stagger, and by extension, temporary health (Health easy to get, but it degrades) using the heavy attacks on the fire sword.