Spend alerts are a post-mortem tool dressed up as prevention. By design they fire after the billing cycle aggregates. The real fix is catching runaway patterns at the config level before they run. That is what we are building at Traeco. The difference between an alert after 28k euros and a flag before the first run. traeco.dev
The warnings firing off hours later is obviously awful design, but the warnings are just warnings. The spend caps are something different and Gemini has them at the very least.
For most use cases where businesses use the cloud hard spending caps are an awful idea anyway. Killing your servers the moment you start picking up loads of new customers is a surefire way to kill your big growth opportunity at exactly the wrong time.
Of course, if you're not planning for sudden massive growth, you'd be crazy to host your stuff with the big three cloud providers.