Motherglare, Anchor, Levia and Scissor showed so many demerits that it's even confusing to define the power scaling.
Motherglare has great feats in the Grand Magic Games, area destruction and high durability. In 100YQ she demonstrated high durability again, but her offensive stats are trash. Her roar didn't even cause damage to armorless Erza, no area damage, no Hax, just defense. One good thing about her is that it took a continent's worth of power to defeat her, but going back to human form was pathetic.
Anchor has great Hax but multiple pathetic moments. Being a water dragon getting hurt by Juvia without even having Dragon Slayer magic? Getting hurt by your own element is already ridiculous, but without DS magic? Erza hurt Irene without DS magic, but she needed a buff from Wendy, and we're talking about Erza, no small deal.
Levia has solid feats since he scales based on Laxus and Mira's power, and he has very powerful Hax. But at the same time, it's bizarre to think that after turning into a dragon, he just threw punches and ripped out his friend's jugular. Among the defeats, it was probably the second most coherent one; Laxus and Mira are no pushovers, together they probably surpass any dragon except Acnologia.
Scissor Runner, I honestly think is misunderstood. He showed up for two seconds, but he looked like the only dragon (besides EB) who was bloodthirsty. He used an area blast different from his partners and had to deal with two high-level mages, not Gray (already tired) and Juvia without DS magic. Scissor's only demerit is not being explored in human form and lacking Hax. Scaling by damaging Mira and Laxus is a great offensive feat that Anchor probably wouldn't have, considering the attack level exhausted him. And let's be honest, it was probably the most coherent death: he was killed by another dragon in a surprise attack, not by learning an enchantment and sucking a continent's power at last minute, nor by getting hurt by his own element.