Without kernel level anti cheat you can detect (some) other usermode cheats, but not kernel level cheats. With kernel level anticheat, you can detect the vast majority of other kernel level cheats. Vanguard is effective enough that most successful cheaters are using external devices and DMA to bypass the kernel altogether (or they just use Macs because Apple doesn't allow Vanguard). And despite Riot's insistence to the contrary, they have not "detected" DMA cheats.