1. both pulumi and crossplane just wraps the Terraform providers as is on many occasions, and quite poorly. There are a lot of pending issues with the dependency graphs, state refresh and proper state diffs. Although a lot of the most troubling issues had been resolved, it's still a mine field run.
2. Both TFCDK and dagger.io can be used for multistage TF deployments, although I prefer dagger myself...
Terraform has a major state management design flaw that had been ignored by hashicorp to force TFE upsales. It's impossible to perform multi stage deployments with a single `terraform apply`. You have to manually identify the deplyoment targets for every stage, terraform providers do not support `depends_on` block and they are not a part of the resource dependency resolution graph. i.e. You can't deploy Vault than configure it with the respective provider - terraform will try to perform both deployment and configuration simultaneously and will fail.
3. This is due to strong Sales Opinion that a Single Plan is of a Positive Product Value for Terraform. While in practice it turned out to be False, the actual Product Value of Terraform is in Single Consolidated Infrastructure state, which can be analyzed by the respective static analyzers (infracost, tfsec, checkov, inframap, driftctl etc). And it's a strong pro compared to both Pulumi and Crossplane...
Having a single state is a blessing for large companies with a tight operational schedule - having multiple states with a single lock can cause conflicts quite often, with volatile outcomes. Yet again, an upsale point for TFE.
Even though Terraform "has more providers" you have to be able to support 'em all by yourself, HashiCorp does not provide a Viable Support Plan for the existing Official Terraform providers (on my xp - maybe someone was more lucky).
That's why I'm often saying that DevOps is not a title, it's a methodology... and every DevSecOps guy should be well versed in golang to be able to support, test and extend the respective tools and operators (k8s automation).
I'm leading the engineering at a startup based in the UK and we actively chose Pulumi over CDK, TF etc....
Been going 12months now and we're really pleased with the decision so far.