I have worked with PT more than you have any idea. (at 52)
Your comment on how quick it dries and how 'not' dense it is after a "few" days makes me question several things about you.. and what quality & where your supply is from.
I can call/Identify a PT piece of lumber by not even looking at it, by picking it up over white pine. by its weight and outer texture alone, days, weeks, weeks, months later.
You are correct about screw holes, and I could see it lasting as you describe. under epoxy or not.
I also understand and have had epoxy flat out rebel from contaminates, first hand.
And PT and especially full ground contact PT has plenty of contaminates.
but all that being said, I have only attempted to epoxy PT 1 time, it did boarder line of "ok" and I questioned how well the "epoxy" would hold up exposed to elements and marine environment.
It is well accepted that PT and epoxy or polyester is not the best mix.
And my experience was not the best either.
So that was my caution extended to a new member with 1 his 1st. comment on this site.