7] 4-A
It comes from the
Final Egg Blaster , Eggman casually built this weapon and attached to the Death Egg to
merely to activate Emerl original program. Despite the time period, this is seen to a very simple thing he built and was not built for any battle porpouses, there could be the possibilty that Eggman can built a battle mech with that same raw power if he was forced to, Eggman most of the times expects to fight Base Sonic not Super Sonic [In Unleashed he planned to drain his power for negative use], later on he would meet his Nega self and built 2-C mechs with him since his Nega self is kinda his successor so he has the resourches to make a tier 2 weapon happen while regular Eggman cannot as Solaris was not his creation and Time Eater was already Low 2-C before being mechanized.
8] The possibilty of scaling
With that said above, in Heroes Eggman
saw Overlord as something that he could not stop as he's combined his data with everyone and was above all his creations, and what could have imagined at the time to stop it as Eggman was betrayed by Metal and immediately thought of the Emeralds [Eggman did not likely quickly gained the thought to concept a tier 4 weapon due his intelligence as there is likely not a big gap of time from Heroes where Eggman was locked to Battle, so Eggman can likely concept said weapon before the betrayal]. In Battle despite happening after Heroes, he built this weapon with no problems and threated it as something not magnificent and complex only as a special weapon for that specific need. In this period Eggman did not saw tier 2 stuff sans Void/Lumina, but this being has no connection with the Chaos Emeralds.
Even if the previous stuff is not enough, the main thing is that Eggman
tested the power of one single emerald and planned to search the others in
Advance 3 since and he knows that the emeralds had great power since they previously stopped Overlord, so there is possibilty that they are higher that all his types weapons at the time since he wanted to search them, again the only tier 2 being he knew at the time was only Lumina and this game takes place after Battle since Gemerl is Emerl successor, also Devil Doom
remarked at 4:00 that he underestimated the true power of the emeralds meaning that they have more power than he had imagined.
9] Who can possibly access it
Fully Emerald Users like Sonic, Shadow, Silver, Blaze, Knuckles, Tails, Mighty, Ray and Overlord via the Eggman stuff. That's what he said all the way back, posted the relevant part
