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.
Of course if everybody quietly agrees that this company is a suitable vehicle for their incompetence, then it's a bad idea to address this. And some companies definitely are.
> 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.
And who's going to fire you for this?
The people telling you to roll this out slowly are doing so mostly to protect themselves from having their incompetence exposed and to appear useful. Protecting them will help them steal your credit and will get them promoted.