So this is purely on an observational perspective but with all that I have learned about the Banished so far in their existence in the universe I see them as a more dangerous threat than the covenant were in certain ways.
- Playing the long game: While The Covenant certainly had massive amount of resources at their disposal they were never able to crush the Banished because Atriox and his followers were able to play smart and were not blinded by the religious ideologies of the covenant. They had big ambitions but used cunning and patience to acquire all they needed and not be defeated by either The Covenant or Humanity. Once the Covenant fell and the great schism occurred the numbers of the banished increased now that there was no huge threats in their way.
-They are more unified: The Covenant lost mostly due to the great schism which greatly affected their forces and allowed humanity a chance to strike back especially with the Arbiter and his swords as their allies. Jul’s Covenant was never truly unified to begin with as Jul was more of an opportunist than a leader wanting to achieve his own goals not caring for whatever his followers desires were. Atriox however has kept a hugely unified force of various species having made promising proposals and has stayed true to his word for most of them. While there are certainly some hateful views between the brutes and elites within the Banished they tolerate each other and Atriox has no quarrel with the elites as does his brutes for they never had a hand in slaughtering the elites during the great schism. How long they will remain unified is unknown but as it stands now it seems they are truly a strongly bonded faction.
-They are cautious and intelligent: They knew the dangers behind all forerunner tech they came across as well as the significant threat the flood posed that they were able to defeat it before it could become unstoppable which is something the covenant never accomplished. They knew what had to be done even if it meant losing valuable positions on the battle field. They are also not willing to lose life meaninglessly due to the pre-mentioned unity and also try not to waste resources on anything that proves to be too taxing. They actually think more strategically similar to Thel when he was still a part of the covenant and was also extremely dangerous.
-They are more violent: While the Covenant wasn’t exactly that merciful they retained some honor in their path of destruction (mainly the elites). The Banished only have honor among themselves and give no mercy to their enemies. They love to conquer and destroy which is something the elites they hire sometimes disagree with but are willing to go with it for the sake of survival and their contract. Nothing holds this group back making them rather unpredictable in their chaos. They also employ new tactics and weaponry such as deadly infusion gels, the deadly blisterbacks and even throwing suicide grunts at the occasional victim.
-They are efficient scavengers: The Banished use a lot of ingenuity when it comes to collecting what many assume would be junk and make them treasures. The Human-Covenant war left behind a lot of things that The Banished have taken and crafted for their own purposes whether it be new weapons or vehicles to add to their growing arsenal. Like vultures they take what they can use and be able to get something great out of it provided no one makes a mistake.