Welcome! Your take is formulated quite respectfully, considering your emotions about the ending. If you keep that up, you do not need to worry about hurting fans
About the specific core of your argument, the "coitus interruptus", I feel you!
Ron likely knew this ending would not land for everyone, but it seems you did feel the (imo) intended disappointment, but not the (imo) equally intended closure, not about the narrative of the Secret, but about that it's fine to enjoy a fictional world to its fullest even if you're aware of its fictionality.
This was definitely risky on the part of Ron, but it's what may have been on his mind since SMI and he wanted to pull through with it. That Thimbleweed Park has a similar ending (and ticks many of the boxes from Ron's blog post) fits with the hypothesis of it being kind of an outlet for Ron's bottled up MI ideas from a time when a Ron-helmed sequel was thought virtually impossible.
There is another quite long thread about the whole game with various opinions and reasoning and many others about specific parts of it, that you might want to check out and maybe some other reads of the ending can add to your perspective, or you'd like to contribute yours
edit: Looks like you got merged into said thread 😁