Does Pantheon E block true damage

Yes it does. Redmercy tested it in his game, on PBE, and ignite's damage got fully blocked.

https://youtu.be/HMG1_H0nGWs?t=1562

It blocks ALL damage, especially tower shots is the most important part. If they are gonna nerf pantheon, i think this is the part they should change to damage reduction, i know currently he can block tower shots, but IMMUNE TO ALL DAMAGE from that direction is a little crazy.

I have to say that this skill is a bit concerning for me.

Looking at his kit, it seems that Pantheon is supposed to be a diver. He has a way in (dash with stun on his W and ult for long range engages), but lacks proper ways to leave a fight.

Divers usually have some tools to survive in the middle of the enemy team. Passive shield Passive shield Healing/Damage reduction Skaarl

But Pantheon's defensive mechanic, his E, seems more like the same level of defensive potency like Skirmisher skills.

The differences: Skirmishers rely on powerful defensive skills and mobility to survive, since they are mostly building damage and therefore are fairly fragile. Divers go for some damage, then tank items, since their defensive mechanics oftenly can't help them survive all by themselves and they also oftenly scale with defensive stats like health.

Now looking at the new Pantheon, it seems that he is a Diver (can afford to build just some damage, then go for tankiness), but also has a defensive ability on the same power level of Skirmishers, which could result in him being really hard to kill.

Currently it blocks ALL damage.

So if you Ignite him and he presses E and you are on the Block side of his shield, he takes no damage.

Same with Malz E or any Burn on him.