I have a question - is +1 supporting value for Archon is correct? In original StarCraft he has +2 supporting value. Why he is so weak? He have more powerfull attack than Tank or Ultralisk! This is a mistake or part of balance?

[sorry for my english]

Yes it is. It was done in order to rebalance the Archon, which was considered too powerful before.

...as was the cost of the Archon, which was increased by one two the finale value of 2 gas.

Yes, but this is because his final cost must be 4 like Reaver or Siege Tank(Leg Enhancements Technology card was used with their cost)

I don't critizise the decision, I simply stated it in case someone hadn't noticed