Yes. Better evidence of a fact is indeed better evidence. And if that is in reference to a key fact, the quality of the evidence can make a difference. So as a general principle, if someone's medical condition is an important factor, yes, good to have better quality documentation than something which might be brushed off as cursory self-serving conclusions let alone potentially falsified.Although I agree with you OP seems to be trying to create a favourable letter from a doctor that describes a serious illness to try and increase chances. If he is pulled into secondary having some more concrete proof that his mother actually has a serious issue would back up a doctor’s note that can easily be falsified by anyone.
And as a general principle, yes, good idea to have stronger objective evidence, qualitatively stronger NOT quantitatively, especially if it is quantitatively small. In contrast, pulling out and presenting a folder full of medical records is not likely to help matters much.
Beyond that getting into the details about particular items of evidence is really tricky stuff and not a subject which can be reliably addressed in a forum setting. Marshaling evidence to make a persuasive case is what high paid experienced trial lawyers do. Few of them ever touch immigration or citizenship cases.
Short of that, short of obtaining the assistance of an experienced trial lawyer, which would be difficult to do even if one has a brother who is one of those high paid experienced trial lawyers (they tend to be less than interested in such matters as this), what appears to work best the most often is to simply be prepared to openly, honestly, fully explain the situation, the what and why, mostly in one's own words.
Which yeah, tends to leave those who have not been genuinely engaged in making the move on the downside of the equation. The best they can do is to be making the genuine effort as soon as possible. And for them the open, honest, genuine explanation of what and why is still the best bet, their best chance.
If their objective is just to hold on to PR status without actually, genuinely trying to make the move to settle PERMANENTLY in Canada, that's a different ball game. What I have to offer will not help them much. Most of what others in this forum offer will not help them much. And CBSA officials appear to be more capable of recognizing the difference now than it seems they were just a few years ago. Most signs indicate they are looking closer, and that they have more tools for identifying who is being evasive or deceptive.
Indeed, there appears to be significantly more recent IAD cases addressing misrepresentations in PoE examinations than we saw in the past. Among the most commonly caught misrepresentation is the PR who reports having last been in Canada more recently, in the customs declaration, than the PR actually was. Not sure how it is that CBSA officers are catching this, but it is readily apparent they are in a significant number of instances.
In any event, typically the outcome of the PoE Secondary examination will be far more influenced by the two key factors: how much in breach the PR is AND the officer's impressions about the PR's credibility, the officer's impression about how honestly the PR has been and to what extent the PR has made a genuine effort to get to Canada as soon as reasonably practical and is genuinely engaged in an effort to settle in Canada PERMANENTLY.
Other details can influence things some. But those two mostly dictate how it will go. If the officer's perception of the PR is that the PR is an honest, genuine immigrant doing his or her best to make the move to Canada, not playing games, not being coy let alone deceptive, the officer is likely to readily accept even a very brief letter generally referencing a family member's medical situation. In contrast, if the officer is skeptical, let alone outright suspects some fudging of the facts, a so-called mountain of evidence is not likely to help much.
After all, it does not really matter how seriously ill a PR's parent was or wasn't. That does NOT excuse a breach of the RO.
There seems to be some widespread misconceptions about H&C factors related to a family member's health. The RO itself is intended to accommodate these things. Allowing three years of absence is expected to be enough to meet a PR's need to go home when a parent has a serious illness. More time abroad than that suggests the PR's priorities are inconsistent with keeping PR status.
In contrast, if the situation with a parent or other matter in the home country is something that merely delayed the PR's plans, and the PR has reasonably, genuinely been in pursuit of making the move to Canada, so far it appears that PoE officials are still showing some lenient discretion and allowing some the opportunity to stay without being Reported. No guarantees. We do not know the statistics. We know some are treated with much leniency. Some not so much.
Bottom-line: the sooner the PR gets to Canada, the better chance of keeping status; and the more HONESTLY the PR is prepared to explain his or her situation, the better chance.
Bringing this around, finally, to the idea of "creating" evidence. Asking a doctor for some documentation is one thing. "Creating" evidence is another. The implications are obvious. And CBSA officers are not blind. They tend to see the obvious, and know it for what it is, more often than not.