They are only too strong vs t1, vs t2 they are fine. They can get slightly weaker vs t2 as side effect, they will still dominate it, exception is the chickenbot, that would need to get adjusted to a obsidian that is weaker vs t2. And that they are to good vs t1 can be seen in the replay i posted.
In my tests i haven't seen shields beeing too strong, but in real games its a different situation. Shield strenght isn't easy to see just in tests. I had some concerns to the shields, but with the shield stacking panalaty (that im still not a huge fan of), the easier to spam shields are actually not so good. And Zep wanted the shields to be strong, i don't see a problem, as long as the shielded units are a bit weaker instead. But obsidian is too strong for that (yet energy cost increase will be much less troubleing then speed nerf) and the blaze still too weak.
i think there might be a solution to both of these problems, but im really not sure.
it would be making the dmg per shot 500.
As said, the value of shields is hard to see. In straight equal mass fights they lose, but you never have theese ingame. Afaik ishies vs obsis look quite good, ishies can win with kite (the reason why speed decrease on obsidian would be a very bad idea), but lose without (dont get confused by the shield test). Thats why i thought 720 dmg will be good, it won't touch the ishie/obsi balance, and the little nerf vs pillar/rhino won't really make a difference, they still own them hard. 500 HP would make it really OP vs pillar, and also won't really reduce its effectiveness vs t1.