I think you forgot one of the things the Constitution assumes:
That people are basically evil. That’s why they built into it an elaborate system of checks and balances to keep evil at bay. Enlightened self interest of the offended branch of government would assert itself to stop the offending branch. Tyranny would then be impossible if the branches just asserted their constitutional powers.
That worked until the legislative branch caved completely to the judicial branch. The judicial branch now has far more power than the constitution envisioned, and the legislative branch, the only branch that could constitutionally stop them, is nowhere to be found.
I think the fundamental flaw is that the legislative branch has no “self interest”, just the individual members of that branch have their own self interests. Each congress critter is only focused on amassing power, money and favors for themselves. They could care less about the standing of the entire branch in the overall scheme of things.