Cobra deserves more respect.
He was an antagonist who was never actually defeated in a fight. Cobra was able to match and even surpass Natsu in hand-to-hand combat with his Hearing magic. And that's before he turned on his dragon slaying magic. Natsu was thoroughly outclassed and got played like a fiddle. It was only by pure dumb luck, when Natsu let out a scream in sheer frustration of his helplessness did Cobra eventually fell. Despite so, Cobra quickly got back up to his feet and was the last man standing in their fight.
Hearing magic and poison dragon slaying magic might not be the most visually impressive or destructive types of magic. But they sure as hell make a highly effective and dangerous combination. His hearing magic enables Cobra to read his opponents' attacks in advance and respond accordingly. While the poison from his dragon slaying magic gradually eats away at their health and mobility/motor coordination. Simple, yet deadly. Had
plotBrain not interfered, Natsu would've been the one gotten murdered instead.
They are clearly not the same. Brandish held August with great respect and high esteem, referring to him as her grandfather. Brain had absolutely zero respect for the members of Oracion Seis, ridiculing Cobra for his 'defeat' and belittling the members of Oracion Seis as mere pawns in his plans.
Cobra did not back stabbed Brain. That was as direct a frontal assault as any. Brain had betrayed Cobra previously, and if Brain had even an ounce of self-awareness, he should've known Cobra is not going to fall for his words again.
Now, this
is a legit back stab.