This is undeniably true, and Kakashi appears to be getting cooler and stronger as the series proceeds. By the time Kaguya Otsuki strikes, Kakashi has grown by leaps and bounds and even utilizes the Mangekyo to create Susanoo. However, it must be noted that Kaguya is a goddess, so her strength may very well be beyond that of a human being. Now, as for how strong Kakashi actually is, we can't say for sure but he seems capable of handling himself against some pretty powerful people. For example, he fights Obito almost as an equal and defeats him with one hand tied behind his back. Also, when Nagato uses Tailed Beast Mode on him, it looks like something that would take someone extremely strong to pull off. Finally, when Sasuke Uchiha attacks him with a Rasengan, they both end up in hospital. But anyway, you get the point. As for Kaguya, she's already mentioned that she's a goddess so there's no way to know what kind of power she has except to assume it's greater than anything else on Earth.