Oh, I absolutely agree with you on the probable outcomes if America did implement structural changes these days. That has like a 1% chance of actually being something positive. I think perhaps the most recent, best possible time for significant reforms was somewhere between 1930-1990. It depends mostly on the specific kind of reform (basically whether or not women or minorities were relevant to the change, farther in the past would be worse outcomes for them).

But some things like campaign finance reform, how many seats there are in the House, Supreme Court Reform, etc could've been accomplished with a relatively high likelihood of positive outcomes.

Basically before the complete collapse of proper journalism, when broadcast media was still king and most politicians still tended to compromise and were at least mostly interested in actually governing. It feels like post 90s, our governing body has passed some sort of tipping point where the majority of members are simply gaming the system, obstructing others from actually doing anything and shooting down any and all reasonable compromises. The actual productivity of Congress seems to be in total free fall. Bad actors pretty much always existed, but they only became a crippling number somewhat recently. (Or at least this seems true for the last 100 years, I have no idea if Congress was this dysfunctional in the early 1800s or something)