I have always wondered what is the actual reason behind Blackbeard attacking Baltigo after Burgess found out about the Revolutionary Army’s headquarters. Although Burgress implied that there was a large weapon stash on the island and they should target it. However, he was unaware of the discussion of Wine Steel(Drunken Iron Ore) that happened between Koala and Dragon, and weapon alone doesn’t fully justify attacking the Revolutionary Army’s headquarters.
Burgess informed Laffitte and Shiliew that he was on an unknown island and it happened to be Revolutionary Army’s headquarters, and Dragon/Sabo were located there. It is interesting to see Shiliew’s reaction as he was more interested in where Burgess was located rather than the weapon stash he was mentioning.
After Marineford Arc, I humbly believe that Weapons in One Piece doesn’t really add up to any particular crew’s strength(barring Capone Bege crew) and its impact on the Marineford saga.
Also, Going after the devil fruit that Sabo/Dragon possess doesn’t really add up after recently losing Mera Mear no Mi and Dragon’s fruit still being unknown at the current point in the story. If Blackbeard’s crew were interested in weapons, they would have easily accumulated tons of weapons after capturing Whitebeard’s territory as war spoils.
I believe the intention behind the attack revolves around Road Poneglyphs, although not implied strongly, I, however, believe that the Revolutionary Army is in possession of Road Poneglyph’s copies, through their immense connection in the One Piece world and they are the main opposing force to World Government at the moment, plus dragon being given World’s Worst Criminal moniker makes it a valid argument that he holds at least two Road Poneglyphs copies or more barring the lost one.
To support this point, I do believe that reason behind Robin being transported to Baltigo makes sense, however, Robin declined or she has not shared the information regarding Poneglyphs by the Revolutionary Army. It is evident from the fact that Robin wants to know about the history of the Void Century through her own adventure with Luffy sharing the same idealogy.
Blackbeard who is touted as the roadblock for Luffy becoming the next Pirate King, really doesn’t add up that he is not after Road Poneglyphs, whereas the latter has already acquired two and is on verge of getting another one after the current arc conclusion. At this point in the story, where there is a race to reach Laugh Tale first and unearth the last hidden Road Poneglyph, Blackbeard being inactive in the pursuit to reach Laugh tale doesn’t gel well with his current plan.
Thus, to conclude my theory, I believe that Blackbeard attacked Revolutionary Army in hope of finding the Road Ponelglyphs or at the very least acquiring the information about their whereabouts (the latter I wholeheartedly don’t believe as he served in WhiteBeard’s crew and should have some info on the location).
TL;DR: Blackbeard attacked Baltigo to acquire Road Poneglyphs copies that I believe Revolutionary Army possesses.
Let me know what you think about this and please feel to criticize or add to the theory if this whole ordeal makes sense to you.
Theory by RuncornThristle (https://www.reddit.com/user/RuncornThristle)