Indeed, forums can be run however the founders wish.
I certainly do not think that, sorry if something I wrote made you think that. There certainly is no reason for anyone to have entitlement to waste moderator time, and if that seems to be a member’s intention suspension and banning may be the best choice.
Seems that you had problems with immature members who were questioning decisions excessively such that the policy to not allow appeal of mod decisions was implemented. That may be reasonable if you have really good moderators. There also seems to be a potential risk with that, such that if their authority cannot be questioned, that could drive some members away who could possibly be a benefit to the community.
I do agree with your policy of not allowing arguing of mod decisions in the topic where those decisions were made. That could definitely completely derail an entire conversation I imagine. If someone disagrees with a mod decision that can be something worth talking about in a different topic or non-public message to clarify where there are different perspectives.