To be honest, I’m still a bit confused about how this works. Is it correct to me that if the employee does not fulfill the Service Objectives, this will be practically (though not legally as the US usually has at-will employment) be seen as grounds for termination? If so, then to me it does feel like less job security than most jobs in-practice have, though maybe a) legally this is not true, and b) normatively the standard advice is that orgs should be more willing to fire than they in practice have.
Hmm, I think the question of whether employees should have objective requirements is somewhat orthogonal from the question of whether they should have a tour of service. For example, many salespeople have sales quotas, despite not being on a tour of service.
That being said: the alternative to having objective requirements is something like “you must fulfill the whims of your manager” and it’s not obvious to me that this is actually better for job security.