Hmmm...you're still choosing among a set of systems that were also designed to manipulate human psychology, but survived a few centuries, potentially getting refined.
One argument is that a system that survives that long can't be full blown toxic (would destroy itself in the process), but it's still not guaranteed to be better than any other system that also aren't full blown toxic (include one you make up by yourself), until you dig really deep into it.
To take an example from another field, full-blown royal/aristocracies government went on for centuries in France, and the country was quite successful from several metrics. But looking back we wouldn't argue it was a pretty nice system that could still be chosen today, just because it wasn't outright toxic.
One argument is that a system that survives that long can't be full blown toxic (would destroy itself in the process), but it's still not guaranteed to be better than any other system that also aren't full blown toxic (include one you make up by yourself), until you dig really deep into it.
To take an example from another field, full-blown royal/aristocracies government went on for centuries in France, and the country was quite successful from several metrics. But looking back we wouldn't argue it was a pretty nice system that could still be chosen today, just because it wasn't outright toxic.