Yes Pulumi is nice. Having the power of Typescript types (if you choose Typescript) is amazing.

The thing is I haven't used Terraform extensively so I can't compare.

The main downsides I found are probably IaC downsides in general. Such as scenarios where you need to click-ops to repair because only some of the infra was deployed. I think the clouds need to make their stuff IaC friendly to avoid this though.

My main fear is taking on that dependency on something newer. With Terraform if the company goes bust, the community could take over, and probably it would become an Apache project. Maybe Pulumi would too. It is not good enough for it to be open source. It needs to keep up with the daily changes in the cloud.