A three week holiday abroad will not have any significance in the assessment of a citizenship applicant's qualifications. That said, timing can be a factor. Missing scheduled events can lead to concerns or even suspicions. Missing the oath can result in the application being deemed abandoned. So it is important to timely get communications and be able to appear for scheduled events (tests, interviews, responding to document requests, the oath, and such).
Assertions that IRCC will exercise its discretion capriciously or abusively are hyperbolic. Pure horse pucky some might say.
There are exceptions, isolated incidences, as there is in the decision-making for any large bureaucracy. Applicants make mistakes, like failing to completely and accurately report every trip abroad. Bureaucrats also make mistakes. Stuff happens. While a few isolated incidents have fueled some of the fear-mongering criticism, those criticisms remain largely unfounded, gross exaggerations at best.
Mostly IRCC has a large workforce making a concerted effort to do a difficult job. Some of the decision-making depends on making complicated inferences affected by many diverse factors, and is simply not simple or easy. In contrast, many disagree with some inferences CIC/IRCC has made, failing to recognize that appearance and impression are important; there is this false belief that it is unjust for CIC to have made an inference if the conclusion is not true. That is not how assessing evidence works. CIC/IRCC does not have a crystal ball and cannot know what the truth is for sure. It relies on what the evidence is and what are reasonable inferences based on the evidence. Life, however, does not always follow an obvious path. So inferences can be wrong. CIC/IRCC cannot guarantee to always get it correct. They will sometimes get it wrong. But CIC/IRCC makes a concerted effort to make reasonable inferences, and the idea is this will minimize wrong outcomes.
Nonetheless, remember, the burden of proof is on the applicant. If the applicant's evidence leaves room for variable inferences, that's on the applicant, even if CIC's inference is not correct.
As for the intent-to-continue-to-reside clause, no it is not subject to widely varying interpretations. Claims to the contrary are more of the same red herring malarkey that has been a distraction now for two full years.
Yes, residing abroad while the application is pending is likely to cause a problem if and when IRCC perceives it. Frequent or extended absences might trigger elevated scrutiny. Working abroad will almost certainly trigger elevated scrutiny. This was true long, long before the new law took effect.
But an applicant who has a routine case is not going to encounter problems just because he went abroad for a three week holiday . . . again with the caveat about being sure to get notices from IRCC and being able to appear for scheduled events.