To answer your question the barksdale crew weren't looking to take over the streets of Baltimore, just maintain the towers. Barksdale daddy was in the game, the whole family was. What you nikkas talking about "garbage ass goons"? Wey Bey was solid, all them nikkas was, well the original crew anyway. Come on breh, did you see the way they did Omars boy, they were loyal, put in that work on the nikka. Wey Bey must have had at least 20 bodies on him. Bird was a goon too. Even Cutty, when he was in the streets.
Marlo, was patient, he knew when to strike when Barksdale crew was weak. When the towers came down, it was a free for all in the streets. But he got drunk with power, killing nikkas just to kill them.
They killed D'Angelo, because he kept fukking up, first by catching a case with shooting in the towers, then writing shyt down apologizing to the family of the guy who got shot, getting the stash stolen by Omar. They don't know what he was going to do, he could have gotten tired of serving 8 years and tried to get his sentence reduced. Remember Barksdale was invisible to the police up until that trial, so I bet Avon was like what the fukk is going on. He had to get rid of all the factors, the security guard lady, D'Angelo, and of course Wallace.