How pointing a jump ability from outside of heavy bolter range right on top of them and hardcountering it this way is harder then walking up to MG?
And since you're talking about killing gunner and not actually throwing a nade, then let me remind you this again:
Only one faction got obersoldaten and their power level over 9000 will get reduced to normal human strength in 3 days.
Jump Assault Marines into Shuriken
Banshees say Hello bonus dmg vs Power Armour
Bonus melee damage vs retreating squads
Lose EXPENSIVE models on retreat (from a 3 man squad!)
Run Rifles into MG42
Throw Grenade
Retreat
Lose 0 or 1 (or even 2, if you want to argue) model(s) from a 5 man squad because suppression reduces damage dealt
Jumping a squad into melee range is significantly more risky than throwing a grenade from 300km away with grenade bulletins.
"But derpface you have banshee + Shuriken vs Assault Marines, but only rifles vs. MG42!!"
Assault Marines = 500 req 50 power
Banshee = 400 req
Shuriken = 240 req 30 power
Total = 500 req/50 power vs 640 req/30 power. Not identical, but somewhat similar. 20 power for 140 req isn't an unreasonable difference.
Rifleman = 280 MP
MG42 = 240MP