Look at Iron Man's weaknesses, he has none, not in the conventional sense but if what you're claiming is true, then apparently some can be found. Exact same situation with the GL I'm guessing, the fact still remains, that BB's blasts were tailored to burst through a GL's energy shield. But, lets entertain the other side. BB did it out of pure force. BB's strongest attacks are city destroyers. As we all know, GL rings are more than capable of tanking city destroying attacks. Alos, there is no evidence of him using magic to bolster his energy blasts as you claim. If you showed me a scan of BB draining magical energy from the ring or something, then saying/thinking Im gonna use this, then bursting through GL's bubble, my point is moot. There is also another way you can prove this, BB blasts do not get through GL's shield the first time, he absorbs magical energy, they get through the second time, your point is now proven. I however, have evidence from the Wikipedia saying that BB cannot bolster his attacks with magic as the Wikipedia says BB can ONLY percieve disrupt and absorb magical energies. This would also give evidence that BB's blasts are magical in nature, and as thus, being able to blast through Iron Man. But I sincerily doubt you have the evidence.
"the GL rings have exactly 4 weaknesses. and only 2 that could be used to blast through a GL energy shield without the use of superior power. 1. Willpower. ie. disrupt the willpower of the wearer. but as you yourself have pointed out, the Scarab has no effect on the minds of its opponents. it cannot perform mindcontrol in any way. 2. Red Power ring Energy. ie. GL rings are weak against the energy that comes from a Red Lantern ring. however, the Scarab can copy/imitate This kind of energy, just as much as it can copy Magical energy.
that leaves 1 of 2 options. 1. the Scarab is incapable of copying energy that it hasn't already absorbed(aside from various types of regular radiation like that coming from Kryptonite), and it blasted through the GL shield by pure superior power. or 2. the Scarab is actually capable of copying/imitating forms of energy that it does not have available, or have even encountered before. which means that it used Red Lantern energy to blast through the GL shield."
this leave you, with 1 question. can the Scarab use Superior Power(in which case it can blast through Iron Man like he wasn't even there), or can it Replicate/Imitate various forms of energy(in which case it can copy/imitate magic and bypass iron mans defenses) ?
The feat I referred to above, with Stane's suicide bombers, was done with the Extremis armor. It tanked a nuke without any energy shields.