I am... not so sure about that. My understanding is that the Krogan had enough mad scientist types to provide them with armaments technology and ships. Sure, it might be of low tech relatively, but Krogan favor heavy armor, sheer fire-power, and before the Genophage - high numbers. That's enough to cause trouble.
Essentially, with their numbers they are almost as dangerous as the Zerg, the Orks of WH40K, or indeed ME version of creepy crawlies - the Rachni.
The krogan never surrendered a battle, which means those battles where the krogan were defeated were fought literally to the last krogan before allied opposition could claim victory.And they had enough of a navy that they were able to drop asteroids onto turian colonies. This is mentioned a few times, and this tactic (according the codex, anyway) left at least three colonies uninhabitable. That's not an enemy that one merely concerns themselves with in a ground war.
That's essentially three dextro-garden worlds ruined because the krogan were using asteroids for orbital bombardment. If Primarch Victus is not being overly dramatic, the moon of Menae around Palaven is essentially where the turians were holding the line against the krogan before the genophage began dwindling the numbers of krogan reinforcements to the point that the battle in Palavan space was not winnable for the krogan forces. It's a fair bet the turians felt certain the krogan were going to toss asteroids, or pieces of the moon if Menae fell, at Palavan and ruin it as well. It would be for humans the equivalent of losing Terra Nova, Eden Prime, and Bekenstein to orbit bombardment and our navy is desperately trying to hold the krogan back at Luna to prevent them from launching rocks in our asteroid belt toward our home planet.
It's easy to sit and judge the horror of the genophage through the eyes of Wrex and Bakara, but they are not representative of the krogan of that era. If anything, the krogan of the Rebellion were closer to Wreav in spirit than anyone else we met as Shepard. And if you think Wrex would have been the Wrex you know had he been born prior to the deployment of the genophage, I think you're being terribly optimistic.The more likely scenario is without the horror of the genophage to change his perspectives, Wrex would have been just like the other krogan of that era, and perhaps even more ruthless.
It's difficult to fathom the scope of the enemy and how badly things were going for the Council races at the time until the genophage was deployed. If anything, it's amazing that the krogan actually surrendered at all, given their tendency to fight to the last soldier prior to the genophage deployment. WIthout the genophage, they would have wiped the turians out as assuredly as they tried to wipe out the rachni.