"Hey, I wanted to raise up my concerns about X. I mentioned it to (manager), but I'm not entirely certain I communicated it effectively. If we don't do Y, Z will happen". Expect upper management to talk to the manager about it, and expect the manager to try and downplay the concern (or if they're treacherous, express outrage that you didn't talk to them about it; have proof of the conversation if that's a concern). If it doesn't lead to change and blows up, it will be noticed.
Better still - if you have anonymous surveys (most companies do), lambast the manager there (politely), and you place the impetus to change things on upper management there (provided a majority on the team agrees).
The reality is that upper management put the manager there -because they trust them-. They barely even know you. That's the reality. You can still talk to them, but you can't come off as though you're trying to undermine your manager. If upper management's response is to tell your manager "deal with it", you clearly came across as trying to undermine your manager; you're a problem. You just made it so it's your job or your manager's, since you just burned that trust, and in a public way that upper management is now aware of. A good manager will fire you because of the effect you're going to have on team morale. A bad manager will fire you because they feel threatened.
This isn't about what is hypothetically better, this is about what the reality is. The reality is that management is all about trust (really, working in groups is all about trust); upper management has to trust middle management, and middle management has to trust the ICs. Your bypassing your manager is going to look like a breach of trust with your manager (i.e., why didn't you talk to them and work it out with them?). Your claims may be right, but being right doesn't equate to being effective, nor does it excuse being stupid in what you do about it. This guy not only doesn't sound in the right, he also was stupid in how he approached it.
As a slight addendum, too - the reality is that managers that are 'stupid' may still be valuable to higher ups. The business is not evaluating managers the same way ICs are. If the manager makes a decision, overruling the ICs, and the ICs raise their concerns about the decision (NOT the manager), carefully, politely, and the decision leads to a bad outcome, upper management will notice. But I've had decent managers who were technically a bit clueless, but who knew to let the ICs make the decisions themselves; the team succeeded. You can have stupid managers who still run effective teams; if they're actually bad managers, upper management will notice. It may or may not be before you've made plans to leave yourself, but the reality is you can't force a manager to be replaced; you can only work to move yourself (to another team, or to another company), or wait for it to be noticeable and be careful to control the narrative.