AB,
Most of the fallacies you try to identify are labelled as such because they are not water-tight arguments...
No. It's not that they are "not water-tight" at all; it's that they're flat
wrong.
...,but this does not necessarily imply that what is being argued is wrong.
No-one says it does. What it does do though is to falsify your reasons for thinking it's
right.
In many cases they are just indicators to what is likely to be true.
No they're not. Flat wrong is flat wrong is flat wrong. A flat wrong argument for "God" no more "indicates what's likely to be true" than a flat wrong argument for leprechauns "indicates what's likely to be true."
When discussing spiritual matters, it is not possible to express everything as hard irrefutable facts.
When discussing "spiritual matters" it is though necessary to demonstrate in the first place that there is such a thing as spiritual matters at all.
Why not finally give it a go?