1)It means my employee whom I gave a job offer can travel and go anywhere without my knowledge after landing?
Yes. But do you think the applicant's goal is to just travel around? after spending tens and thousands of dollars. If the applicant is holding a restricted open work permit. Then he/she is expected to fulfill his/her role under the same NOC code ONLY until he/she gets qualified as a PR. An applicant with the right set of mind will not opt to look for another employer, knowing that someone is already waiting for him/her.
2) If point 1 is correct, then how can I withdraw my job offer?
You can directly notify the applicant since you are under no obligation to fulfill the contract, should you think that you no longer need the service.
3) They are able to spend thousands of dollars in process only after getting job offer and I am the one who is able to give job offer because I can prove in tax returns that we as a couple are financialy capable.
For your concern "process for all applicants is already stringent" you see it as backdoor to immigration while employer ( e.g. me) see it as exploitation for genuine employers.
Again, if that is your point of view, I respect that. However, you cannot generalize ALL applicants, that we are all scammers for having the same intent. These applicants would want to have permanent resident status and be a citizen. If you have read the details outlined on the government website, there are a series of requirements to obtain that status, and It's not just based on a job offer alone. We are not the ones who roll out the rules and qualifications.
If you think that applicants would take advantage of the employer for this reason alone, I would have to disagree. Yes, we may have spent thousands of dollars on the application, but we are not millionaires. If we were, we would've opted for a student visa or express entry instead of this ridiculous pathway,