Not to say that it isn't, or that it even is for that matter. I recently got Thunderlord out of a legendary engram (lucky me).I generally see a lot of negativity around SGA and good things about TL. I haven't unlocked its signature perk yet, so it's not at its full potential and i'm not in a position to properly compare the two.
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The only time SGA stands out among other high rate of fire MGs is during oracles. Besides that its a waste of both a heavy and exotic slot in both PvP and PvE. I might be a little biased tho