A bit more info is needed for an accurate assessment. How do you measure your draw length, right or left handed, are you sure you are getting a clean release, is there any contact with the shelf or side plate, are you shooting off the shelf or an elevated rest, where is your brace height and nock point set, are you using one or two nock points, do you shoot split or three under, are you paper tuning with a bare shaft or feathered arrow, how far away from the paper are you shooting, is there enough clearance from the paper to the target, what is the center shot of the bow cut to, what type and condition of string is on it, etc.?
There could be a multitude of things happening here.
With the info you have provided, my first thought is that your arrow is indeed too stiff. A 30" arrow for a 26" draw seems a little long. I would bet that the paradox of the shaft is out of sinc with the bow at that draw length, causing some contact somewhere and giving misleading results. Plus you have an internal and external footing that are compounding the stiffening acts of the footings.
If I were you, I would try a 600 shaft with the same set up. If it shows weak, you know that you've made progress. You can always stiffen them more by shortening the length, or increasing the footing lengths.
When trying something that should work and it doesn't, then try something that shouldn't work!
I have found that the axis shafts stiffen up greatly with footings.
Out of my 51#@my 28" Elkheart, I shoot 29.75" axis trad 500's with 150 grains of brass HIT insert and 125 grain broadheads with good results.
You are shooting probably 2#s less, with 2" less power stroke. I hope I helped a little. Good luck, and let us know what works for you.
Ps your nock height requirement may change when changing static or dynamic spine of your arrow.