score:4
is there a general rule as to whether the more restrictive rules will be applied?
No, that depends on the policy of the final destination country. Some care about countries you've transited through, some don't. Most don't care. Countries may change their policies anytime.
E.g. Morocco currently cares (mirror):
Travelers from List B countries, which includes those simply transiting a List B country, must be fully vaccinated AND present a negative PCR test administered within 48 hours of the date entering Morocco
[...] Unvaccinated or incompletely vaccinated travelers from countries on List B must undergo a 10-day quarantine on arrival at a hotel. Please see the βCountry Specific-Informationβ section above.