This is a deep misunderstanding of human psychology.

> the top of the company should love because a) you saved them a ton of money

The top of the company is probably already rich. Being richer is great, but one of the few things rich people generally won't burn to run the money-making engine hotter is their own sense of prestige and entitlement.

> b) you identified a pile of incompetence in their company.

Yes, and you told that fact to people who were already responsible for identifying that, which means you just told them that they are incompetent too. And that transitively works its way all the way up the org chart.

You would make the whole chain of command lose face and do so in front of the rest of the chain of command. It would be career suicide.

Every manager would rather silently waste money than be made to look like a fool. Because the money comes out of the business's bank account, not theirs, but looking stupid affects their personal reputation.

That sounds like a very nice and theatrical outcome, but in reality nobody wants to believe they've been horribly wrong about their understanding of things, which means the higher-ups are going to be talking directly to the managers to get their side and figure out how they can show you've misrepresented the situation. They're not going to fire managers en masse because the new guy said "Everyone here is dumb and cowardly," even with evidence.

this assumes that the "top of the company" is a shining tower of competence, blissfully unaware of how incompetent the people below them are.

more likely, the top of the company is just as incompetent but has lucked / gamed their way into promotions anyways.

So this engineer throwing his managers under the bus may be good for the company in theory, but to the senior management this is a red flag. they don't want engineers who do this - they want engineers who give credit to their managers. if they promoted this engineer and fired everyone else, he'd come for them next.

It would, I replied to someone else below to explain why. But in general, it's best for your future career to be remembered well.