The platform team you describe sounds more like DevOps ("upgrades, CI + CD, ....").
The platform teams I've seen at scale are more focused on providing APIs and services for a business domain. Such as, you can have a platform team for KYC/KYB that develops integrations to document verification providers, and then have stream aligned teams that sit on top of that platform and use it in a product to onboard users. Or in payments, a platform team can manage all of the underlying banking integrations, and then a product team can use these APIs to develop a product that lets users pay for things online. I once managed a platform team that managed the internal ledger for a virtual wallet/venmo type company. There weren't many product features there, but they had to deal with scaling our transaction processing capacity, ensuring idempotency of money transfers, and providing an easy to use API for product teams to integrate with. For more academic/research minded software engineers, it's an awesome team to be on.
You stopped just before the bit that made your comment pointless, the very next words;
> making frameworks, writing scripts, improving developer experience PLUS you are the backstop for the full backlog of every other team so need a lot of domain expertise
The platform teams I've seen at scale are more focused on providing APIs and services for a business domain. Such as, you can have a platform team for KYC/KYB that develops integrations to document verification providers, and then have stream aligned teams that sit on top of that platform and use it in a product to onboard users. Or in payments, a platform team can manage all of the underlying banking integrations, and then a product team can use these APIs to develop a product that lets users pay for things online. I once managed a platform team that managed the internal ledger for a virtual wallet/venmo type company. There weren't many product features there, but they had to deal with scaling our transaction processing capacity, ensuring idempotency of money transfers, and providing an easy to use API for product teams to integrate with. For more academic/research minded software engineers, it's an awesome team to be on.