"Guaranteed" has different tiers of meaning - both theoretical and practical.
In many cases, "guaranteed" just means "we'll give you a refund if we fuck up". SLAs are very much like this.
IN PRACTICE, unless you're launching tens of thousands of instances of an obscure image type, reasonable customers would be able to get capacity, and promptly from the cloud.
That's the entire cloud value proposition.
So no, you can't just hand-waive past these GCP results and say "Well, they never said these were guaranteed".
Ignoring the fact that the results are probably partially flawed due to methodology (see top-level comment from someone who works on GCE) and are not reproducible due to missing information, pointing out the lack of a guarantee is not hand-waving. The OP uses the word "reliability" to catch attention, which certainly worked, but this has nothing to do with reliability.
This isn't actually true, even for tiny customers. In a personal project, I used a single host of a single instance type several times per day and had to code up a fallback.
Try spinning up 32+ core instances with local ssds attached or anything not n1 family and you will find that in may regions you can only have like single digits of them
In many cases, "guaranteed" just means "we'll give you a refund if we fuck up". SLAs are very much like this.
IN PRACTICE, unless you're launching tens of thousands of instances of an obscure image type, reasonable customers would be able to get capacity, and promptly from the cloud.
That's the entire cloud value proposition.
So no, you can't just hand-waive past these GCP results and say "Well, they never said these were guaranteed".