Could you elaborate on the accounting part? I'm deeply involved with billing on all three and while AWS seems to have all the data you're looking for in the CUR, it can be a multi-quarter job to build up the expertise to understand that fact.
GCP has different notions, like multiple credits applying to any given charge but again once you build up the expertise you can work with it. Azure seems by far the simplest to deal with and require the least wrangling.
Shameless plug: At the company I work for (meshcloud) we have developed a freely available model that describes the capabilities your central team is building up: https://cloudfoundation.org/maturity-model/
Disclaimer: meshcloud sells a product for teams in that space
I am part of the central team that manages the provisioning users and accounts and billing.
AWS is miles ahead of how we can express what we want in accounting.
AWS reps are much much more knowledgeable and a pleasure to work with when it comes to billing.