Is spine of the akragaka nearly as good as people make it out to be?

Is it as good as shield block?

This is disregarding vault.

The higher your strength, the more Spine does for you.

When I have taken this edge with a human AP, str 23, it appears to be much better defensively and slightly more offensively with a spear over a polearm with both spear and polearm skill at 100%

Should they not be more equal? I even experimented with enlarge etc.

Does Thunderbolt do anything other than give lightning bolt a chance to deafen, like increase damage?

I tried this as an AP with a 21 dex and 22 strength. I mention that because my understanding is that spinning in general is based on dexterity whereas parry is based on strength whereas shield block is based on skill.

In general, it was not as good as shield block purely defensively. It was not as good as dual wield purely offensively. It was somewhere in between.

Certainly worth taking though if you plan on using vault at all (which you should be, if you plan on sleeping people).

I've had spine on a drow, and it felt like sword/shield was almost always better.

On the flipside, I've had spine on a human with a polearm... and I've felt it was better than sword/shield or anything+shield.

Your mileage may vary.

I've had spine on a giant with a polearm, and it was definitely worse than sword/shield for defense.