You are not overthinking.
Governments tend to oppress and become tyrannical by virtue of having a power coupled with corruption of human nature, unless you have a generation of people like those who rose up and made a revolution in 1776, to found the opposite of traditional state: which is, by people, for the people and of the people. If you think for a moment, we live in dark times now. We are under under constant warrantless surveillance (our data on internet is being monitored 24/7, and Snowden told us how surveillance state works), with no checks, balances and transparency of those who are supposed to be accountable to us. We can not speak our minds freely (if we do, we get banned and thrown out of social media. Real facts or factual debate don't matter anymore, if you go against orthodoxy you are labeled "public enemy #1", and uniformly condemned like "people's enemy" in Trotsky's Russia). And, no wonder, some little brained bullies with badges and guns , in charge of protecting our safety and security, get a whiff of current times and assume they can do to common man whatever they want, do so with impunity and get away with it. So, there is no "overthinking" in anticipating issues or problems when crossing the border, especially if you are an honest, innocent man with no special powers, connections or extraordinary wealth. And, reading hundreds of posts on this forum from people who have been waiting for months for PR card replacement, the possibility that your card won't arrive by 4/22 is not eliminated. Which poses a legitimate question: what do I do if I want to travel to Mexico/Germany/Vietnam and return to Canada, but don't have a valid PR card in time to avoid the hassle?
But, the circumstances of your case are such that you have less to worry than you would under different set of the circumstances:
1. You are not in breach of RO
2. You hold valid PR status in Canada
3. You are visa exempt national in the US, so you can always apply for admission into Canada at land POE, and fly into US from almost any country in the world.
There is nothing border official can do to you, other than being a donkeyhole and showing his true colors. But you can either ignore it or take an issue, report things to his superiors and do whatever you feel you should do (and
can do within legal framework) to make him feel the pain he is inflicting on innocent travelers. But, from practical standpoint, there is nothing they can do to stop you from global traveling and returning to Canada. It's just inconvenient for you not to have a PR card, to fly to US first and then enter Canada by foot or private vehicle (special arrangements have to be made, as opposed to hopping from one airplane into another) and etc.
Have safe travels and enjoy yourself.