We add support when we want to do something new, like MediaTailor + SSAI. At that point we're exploring and trying to get our heads around how things work. Once it works there's no real point in support.
That said, you need to ask your account manager about (1) discounts in exchange for spend commitments, and (2) technical assistance. In general we have a talk with our AM when we're doing something new, and they rope in SMEs from the various products for us.
We're not that big, and I haven't worked for large companies, and it's always been a mystery to me why people have problems dealing with AWS. I've always found them to be super responsive and easy to get ahold of. OTOH we actually know what we're doing technically.
Google Cloud, OTOH, is super fucked up. I mean seriously, I doubt anyone there has any idea WTF is happening or how anything works anymore. There's no real cohesion, or at least there wasn't the last time I was abused by GCP.