Now the question, I need a very strong wood glue for external structural
joinery (6x6 and 12x4 timbers) ... all timbers are tanalized, so must be
able to work on treated wood

In the past I have opted for Cascamite .. it is reasonably gap filling,
strong & waterproof. (and expensive)
But as I have been using Cascamite for more than 25 years has the
technology
moved on ... is there something better ?
I've used Gorilla Glue successfully on (much smaller) joinery on a fence
made from tanalised wood