Force Bubble is repel, repulsion field is knockback. They are different powers. A foe can still use ranged attacks while being repelled, but a foe knocked back will not attack while he is knocked and while he is getting up.
Some people might like Repulsion Field. I personally don't, but I don't think FF is underpowered or underperforming at all, and I think there might be quite a few who wouldn't like the power changed. If you want an ally knockback power, see sonic, it has one, and I don't know anyone who takes it, mostly because of the end costs, though I can see a power like that may have a use or too for ranged squishies.
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Force Bubble is repel, repulsion field is knockback. They are different powers. A foe can still use ranged attacks while being repelled, but a foe knocked back will not attack while he is knocked and while he is getting up.
Some people might like Repulsion Field. I personally don't, but I don't think FF is underpowered or underperforming at all, and I think there might be quite a few who wouldn't like the power changed. If you want an ally knockback power, see sonic, it has one, and I don't know anyone who takes it, mostly because of the end costs, though I can see a power like that may have a use or too for ranged squishies.
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I would be at a loss if my bubblers didn't have Repulsion Field and Force Bubble as they are atm - no doubt I'm in the minority there but still ... 
Some enemies can get past that Force Bubble anyway which is where the field + Forcebolt (and indeed the new Bomb) come into play to stack the kb on the repel resistant enemy.
But I can see where the OP poster is coming from - just have to decide do I want the HUGE aggro inducing large bubble or do I swat things away trying to melee me and then worry about a ton of aggro? 
Hello fellow readers
The issue is the following facts...
Repulsion Field
Projects a field around YOU that repels foes in a very small radius (melee).
Force Bubble
Creates a Force Bubble. When foes try to enter the bubble they will be repelled and powerful foes who enter the bubble will be knocked down. Range of bubble is 30 ft.
Problem: They both do the SAME thing!? Why do we have 2 powers that do the same thing!? Repulsion Bomb was changed so that it effects enemies and not allies directly which means you corrected problems with that power. Now correct the "Repulsion Field" power please!
"Force Bubble" does exactly what "Repulsion Field" does except its a hell of alot better at a small endurance cost which can be reduced anyway (Repulsion costs more if your surrounded in melee).
Repulsion Field should be a ally only buff and repel nearby foes which is what Forcefields is all about, allie and self buffs! The bug is the fact that "Force Bubble" renders "Repulsion Field" near useless (foes dont enter melee range when Force Bubble is active) that nobody will choose the "Repulsion Field" power anyway.
Please consider this change!
Thank you