Frankly, it appears you might not have a good grasp of Canada's immigration policies and practices. It's a huge, huge subject.
Your questions can be at least partially answered by doing some homework. At the least this should include reviewing Section 3 IRPA (see
https://laws-lois.justice.gc.ca/eng/acts/I-2.5/page-1.html#h-274071 ) which details the Act's objectives, such as 3(1)(d) "
to see that families are reunited in Canada" and 3(1)(e) "
to promote the successful integration of permanent residents into Canada, while recognizing that integration involves mutual obligations for new immigrants and Canadian society."
A broader understanding of the Residency Obligation itself should be easily obtained by perusing a few topics here where H&C considerations in relation to Residency Obligation enforcement is discussed in some depth (there are scores of such topics here), or by perusing topics about the available credits toward RO compliance available to some PRs abroad (for example, topics where the
accompanying-citizen-spouse-abroad credit, or the
employed-abroad-by-Canadian-business-credit, are discussed in some depth). In particular, many of us, myself included, have addressed the underlying policies and rationales for them at length and in-depth in many of those discussions here.
Beyond that, reading at least some of the many official sources cited in those discussions, many linked, will help to get a more complete understanding. There are, additionally, other government sources which enable reviewing the legislative history of the legislation, though navigating back to 2001 when the 2/5 RO rule was adopted does take a bit of work. A significant amount of relevant information can be found in older editions of the Canada Gazette
https://canadagazette.gc.ca/rp-pr/publications-eng.html#wb-cont
I have found IAD and Federal Court decisions very helpful. These can be easily found and read at the CanLII Federal website site, here:
https://www.canlii.org/en/ca/ It is easy to search these official accounts of actual cases to find decisions dealing with the enforcement of the Residency Obligation, including its interpretation and application in a wide variety of circumstances.
Attempting to summarize what underlies the policies and practices reflected in the interpretation and enforcement of the RO would likely be more confusing than helpful . . . other than to note its most basic elements: the underlying purpose is to facilitate permanent settlement in Canada, allowing immigrants sufficient flexibility to accommodate almost any contingency requiring the immigrant to spend an extended period of time abroad (up to three years in any five) which is, nonetheless, consistent with the purpose for granting PR.
My sense is that attempts to unravel the precise calculations underlying the two years in five obligation, itself, are not likely to be productive. After all, once the legislation is adopted and becomes the governing law, those details are largely irrelevant in the interpretation and application of the law. In contrast, it is patently clear that the 2/5 rule is intended to be very generous, allowing PRs extensive flexibility in making their move to live in Canada permanently, nonetheless allowing that actually moving to and establishing a life in Canada is not for everyone, not even for everyone who thinks they want to make the move and have passed the screening criteria qualifying them to do so.
By the way:
H&C consideration already allows officials leeway in the enforcement of the Residency Obligation. Rather than some across-the-board "relaxation" of the already, as it is, rather relaxed RO, it facilitates individual specific relief IF and WHEN the circumstances warrant. And it allows officials to deny H&C relief when and where that is warranted. In conjunction with how liberal the 2/5 rule is, that amounts to a rather "relaxed" approach to giving immigrants a lot of options and personal choice in managing the logistics of their move to settle permanently in Canada, and in particular allows immigrants to spend extended periods of time (up to THREE YEARS) outside Canada if needed (need as judged by the PR, not some total-stranger bureaucrat), which is deemed enough to accommodate almost any extenuating circumstances for an immigrant who is (1) intent on settling in Canada permanently, and (2) is capable of doing so.
The latter is a part of the system. Canada has a rather generous immigration policy, especially relative to family unification, but it is not wide open. Immigrating to Canada is not for everyone. And yes, indeed, it can be a hard. It can be impossible for some. Worker-based immigration policies in particular make an effort to screen prospective immigrants in regards to ability to make the move to Canada. But it also relies on the individual to make judicious choices about what will work, what can work for them individually, depending not only on their skills but their financial resources as well. More than a few try and fail. More than a few try and learn Canada is not a good fit for them.
And for sure, there are all sorts of contingencies writ large into the process.
Stuff-happens. A lot falls outside the scope of any guarantees at all. And that is in large part why Canada's PR program allows PRs to spend up to THREE YEARS abroad, virtually no questions asked, to give immigrants sufficient leeway and flexibility to deal with all sorts of hurdles they may personally face in making the move to Canada . . . recognizing, again, the system is not intended to accommodate everyone.
Beyond that,
what-the-law-should-be is a huge subject, and largely an academic rather than a practical one.