Perhaps it’s suitable for the US but in EU we are seeing this for the most of the working day:
"Heroku Support is currently closed. Normal support hours are 9 AM to 9 PM Eastern time. Our goal is to respond to your inquiry within 1 business day. Please note that it may take longer depending on current volume.
Running a critical app?
Heroku's Premium Support offering includes a 24×7 Response SLA and more. Please contact us for further details."
When it is Heroku’s fault (couldn’t access my account with cryptic error message) it is very annoying to be suggested to use paid support, for a product that is already costs more than alternatives.
If it's a Heroku error then they obviously have staff monitoring servers 24x7. Usually I get very quick responses from Heroku Support at all times during the day, regardless of the type of inquiry - either basic questions or platform problems. Obviously they would filter incoming requests. If you pay for support you get a quick er response. If you have a question without paying you might have to wait a bit longer during off-peak (US) hours. But if it's a platform error I'm pretty sure they would filter that out and respond quickly.
And what are you comparing to here? Are you getting instant 24x7 free support from any other vendors? It's quite normal to pay for support in this industry.
As for support I have always found Heroku to respond very quickly. And they do have direct support. https://www.heroku.com/support