To some degree, yes. The ability to jailbreak a phone is indicative of a poor security framework. In theory, there should be a chain of security from the boot

To some degree, yes. The ability to jailbreak a phone is indicative of a poor security framework. In theory, there should be a chain of security from the bootloader, to the kernel, the full operating system that should be secure. If someone is able to break that chain of security, then that demonstrates a weakness in security. The question then becomes how easy is it for an attacker to break that chain of security, and is the jailbreak remotely exploitable.