Pretty nice list, although give the subject it might benefit from splitting up a bit in a series to focus on a topic, main tool and alternatives.
I disagree on a couple of things though.
1. Kustomize is not an alternative to Helm. They are different tools with different goals. Helm packages applications and their dependent stuff (and it so happens it has a templating mechanism). Kustomize is a templating tool by excellence. They can work together and can't really replace each other as long as you need them for their main purpose (if you use Helm just to template your stuff, you're better off with Kustomize)
2. ArgoCD is not entirely fully GitOps. With Flux you setup a repo, deploy Flux in cluster and whatever you put in that repo gets deployed to cluster, as per rules. You can organize your apps in subfolders, etc. You put flux in a different cluster and feed it your repo, you'll get a duplicate. With ArgoCD, you need to setup ArgoCD itself but then also each application you need needs to be setup to point to its repo/folder/helm repo. If you need to move it/replicate/recover, it's still a bit of a manual process. Great UI though.
3. A Sealed Secrets alternative is also SOPS (from Mozilla). Works in the same way, can use a number of encryption backends to allow putting secrets into Git. Helm has Sops plugin and both of them can be baked into an ArgoCD image (plenty of examples, I developed some myself).