[DannyBee]

"Considering we can decide to abolish the constitution in America (or in any country) any time, does that mean we don't have a constitutional republic in America?"

The former is not correct, so the latter is nonsense. The constitution has no provision for abolishing it, the same as it does not have a provision allowing secession.

There is actually even caselaw on this, and it's very clear that it is about a perpetual union.

"Technically we can never say that we have a system X which is not Mob rule because the mob can always abolish it." That is 100% not what has happened here. In the constitutional system, there is a process for amending the constitution. it is not mob rule, or anything close to it. it is possible for basically 100% of the people to be against or for a thing, and them be unable to make it happen directly. (even if they call a constitutional convention, they send representatives, not a mob, etc)

In the other other case, the rules are 100% made up by whoever has the largest mob, directly. That is mob rule.