Yeah I completely understand your opinion on this.
I myself am studying Immigration law. And I have read all the operational manuals regarding processing and assessment of Common law sponsorship.
If our relationship was declared common law in another country (like a country where it is not allowed) then it would have been a issue. But we started our common law and declared it in Canada (a country where it is allowed and practiced).
Like this thing I am taught:
It’s not for common law but still talks about the same issue...
Some marriages may not be legal where they occurred, e.g., defect in capacity (who can marry whom), marriage in embassy not recognized by host country, religious prohibitions, form of ceremony not permitted, etc., but the marriage would be otherwise recognized in Canada. Officers should explain to the applicant that they do not qualify as a spouse because their marriage is not legal where they married, but that they might qualify if they marry in another jurisdiction where their marriage would be legal.
If re-marriage in another jurisdiction is not feasible, and if the relationship between sponsor and applicant is genuine and the relationship meets the requirements of either common-law partner or conjugal partner, they may be processed as such. To qualify as common-law partners and conjugal partners, they must have maintained a conjugal relationship (have combined their affairs, be mutually interdependent, have a sexual relationship, etc.) for at least one year and, in the case of common-law partners, must have lived together for at least one year. Applicants should be consulted before they are processed in another category.
It actually wouldn't have mattered what country you became common-law in. Canada recognizes it regardless of whether other countries do. What matters is the cultural norms of the origin country. As long as you have solid common-law proofs, you should be fine but IRCC may ask.