So the concept of 'bonus turn' vs 'TM gain' is largely to help differentiate what is impacted when facing characters who prevent bonus TM gain (e.g. Malak, Hux, etc.). Those characters have abilities that prevent 'TM Gain', but 'Bonus Turns' bypass that mechanic. Otherwise it'd be even more confusing to players to determine whether or not a particular character's TM gain mechanic would be negated by an opposing character's ability that prevents bonus TM.
Also, you're forgetting that Fear also causes a toon to miss a turn - not just stun...
