Am I in Sub-1:26 Half Marathon Shape?

That is a strange time to aim for

The 800s and ladder look very close to where I was when I ran a 1:26 time trial as a tune-up. I also did a 6 mile threshold run at about 6:15 pace, 7 mile T around 6:25, and a few marathon pace long runs at 6:50-7ish.

i find it hard to predict anything beyond 12km with this or that workout. Too many race day factors, especially with a 1:08 margin.

run under 1:30 comfortably

I think your 6 mile session is likely a good indicator of the pace you can hold for a half marathon.

Provided of course it was a controlled effort and not an all out one.

Why did you do 10x800m at 5:40 minutes per mile?

I run 1:19 half and 36 10K, and I would do 6-8x800m at 6:00. I would do 4x1 mile at 6:10 which is around HM pace.

You are overtraining, being a workout warrior and you will never improve until you train at your CURRENT level of fitness!

You're probably about there. Threshold for 1:25 would be ~6:20 pace. Those 800s are fast but they're not super race specific. Knock out some interval sessions where you're running 6:20 pace for 10k-12k worth of volume. 10-12 x 1k/6-7 x mile on short rest. Do some tempo stuff in your long runs -- 2 x 3-4 miles, 3 x 2 miles. Doing that stuff at marathon effort is fine for building strength. Focus on mileage and more specific sessions and there's a ton more time you can begin to chip away at.