And again you are mistaken:
Lets take it step by step:
1. you are assessed using this manual.
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/permanent-residence/express-entry/assessing-electronic-application-on-section-a11-2.html
2. From that manual you know that you must prove, you must prove to meet CRS criteria for your draw and to maintain it until your E-AOR (until you will send out your application).
3. Your family members are still your family members regardless if they are accompanying you or not, so the exception of not recalculating points if they change their heart in the middle of the process does not apply.
4. Officer is also checking your application for misinterpretation.
https://laws-lois.justice.gc.ca/eng/acts/I-2.5/section-40.html
5. Misinterpretation is also:
for directly or indirectly misrepresenting or withholding material facts relating to a relevant matter that induces or could induce an error in the administration of this Act;
So in case of non accompanying spouse withholding information about true intentions of your spouse (to apply for sponsorship the moment you land and of course always having intention to immigrate). Of course with that lower score with your spouse you would be never able to get invitation for that round, so in other words by making your spouse non accompanying you claim points you should not. So at the end it would produce an error to approve an application that should have been declined.
6. If this double intention is discovered during your application, you can smooth talk yourself out of misinterpretation, but not out of points recalculation.
So yes what you discuss just for the sake to get ITA is a fraud and illegal.