Here is our first detailed report on the new Guild Dwarf armies. As you requested, we are focusing on what we can observe of their military prowess, and leaving speculation about their background and motivations for other times.
These new dwarfish forces use the Walls for attack and defense to a slightly greater extent than the army following Oldin. For starters, the new Summoner Bolvi uses his Stone to draw on his Walls to strengthen his personal attacks. This gradually destroys his Walls, but the short term boost makes it worthwhile to him. If he has all his Walls on the Battlefield he can be truly terrifying in his attacks.
Bolvi is also more directly destructive to the Walls than Oldin is. But this Wall destruction is indiscriminate, hurting his own Walls just as much as his enemies'.
Bolvi is not alone in focusing on Walls; he also has Champions with him who are adept in using them. For example, Dwaf is just as knowledgeable in destroying opponent's Walls as Oldin's Engineers, but he is more dangerous than them since his attacks are more skilled, and he is much harder to defeat.
Even more alarming is Ulfric, who surprised us with how much he has developed Oldin's Stone Melding ability. Ulfric not only protects himself, he can protect the Wall and any friendly Units adjacent to it. What's more, he carries a ranged weapon that looks like it may use the gunpowder invented among the Cloaks.
It has taken some restraint to focus on the Summoner first as you wished. Bolvi's army has brought something unprecedented to the Summoner Wars -- Assault Towers -- and we are eager to tell you about them in our next report.