What I’m trying to understand is whether the support from engineers differs between private users and enterprise users.
Of course they are different. I suggest you to read this How to join the community . Also, you can get it touch with sales that will explain you what you would get with a subscription.
Another point of confusion for me is whether the lack of responsive support for private customers is intentional, pushing everyone towards purchasing a subscription.
Absolutely not. I think you have a completely wrong understanding of what an open source community is. You complain about the lack of responses on some posts: have you ever supported another user in this community?
My wish is to get more people involved to help each other, this should not be intended as the place where people ask questions and somebody from Canonical replies.
Personally, I won’t decide on any purchase until I am satisfied with the trial or evaluation. I think most people feel the same way.
I’m not the guy who should explain why enterprise support is important when running a business!