I just got an AWS cert myself (Solutions Architect Associate) and while I don't have any experience with other certs, I do feel like studying for it helped me get a better understanding of what AWS services were available and how to better design systems using the AWS services. There weren't really any "memorization" questions, the questions were more scenario based - like a customer wants to do X, which one of these services/configurations would make the most sense given their needs for high durability/reliability/cost saving/whatever.

Are certifications a perfect way to judge someone's competence? definitely not, but at least in the case of that certificate I think it'd be hard to pass the exam without having at least some decent knowledge of which AWS services are the best to use in different business situations.

Yes security certs are valuable in some cases, my manager has a CISSP and attributes his current job role to it. I think it also helps people looking for a first job to make up for a lack of experience. It's just a part of the overall consideration though, just having a cert itself won't guarantee you anything. And it shouldn't there is a lot more to being a productive team member.