Anecdote on the other side - Small customer (~5k/mo google cloud / firebase spend). They're support has been decent. Sub 24hr email response and technically competent enough to quickly escalate. It was comparable to AWS basic support.
Usually, it's a case of "You get what you pay for".
For GCP, you can get 4-hour response time SLA for $100 per user. If you want 1-hour response SLA it's $250. Then there's Enterprise Support if you need 15-minute response SLA, TAM assigned etc which costs more.
I have as a Fi and as a One customer, and both services had very good customer support. In the half a dozen time I've contacted them, I got someone helping me within a minute and my issue resolved in under 15. That's a normal Google customer though, I can't speak about Cloud, which is an entirely different beast.