I think the rangers are the only thing I'd change - I'd save the points on them and double the size of the small jetbike squad. Rangers really need a farseer to help them put out damage.
6 Rangers hit on 3+'s = 4 hits. wounding on 4's - 2 wounds. Chances are your opponent will get armour saves against them.
I do think they can do a job camping in your backfields - but the rest of your army is very quick compared to the rangers.
So yeah, I'd drop the rangers and stick another three bikes with a cannon in to make 2 squads of 6. It means first blood is harder to get off you too.
I find most marines players round here tend to drop pod sternguard - they have ammo that ignores cover, whereas the jetbikes will use their armour save and higher toughness. If they use ammo that ignores that, you get to jink.
Good luck in your tourny