The one second delay on her Standing Stone is so that she can't instantly place a bunch of stones on top of someone and then ult them to instantly kill entire teams. Her damage is increased by a massive amount when enemies are near her stones, and giving her the ability to instantly place them at a target area would make her incredibly overpowered.
The massive range on her E is ok because it will very, VERY rarely be used due to the fact that it bounces off of walls.
Despite the fact that her E fires for one second, it only deals damage once (unless split by a stone). The reason it fires for a longer time is because lining up an instant cast ability to properly bounce in the way you wanted it to would be incredibly difficult or require really weird targeting indicators.
The scaling damage and scaling on her ultimate are very low, so that in order to reach a terrifying effect you have to use it properly with stones.
With 600 AP, she has a maximum total ultimate damage of:
250 (+300) base damage
11 standing stones (1 second root + (11*.5) = 6.5 second root), which would put the target in range of the full DOT duration of each stone.
11 stones * 520 total damage over 4 seconds = 5970 (+558000) = 563970 damage, which is a lot of damage. But this would only happen if you had eleven stones stuck on top of eachother and an enemy decided to walk right into them and didn't get out of your ult during the cast time (which is the same as zyra's ult), and as such could only really happen against bots.
Each standing stone has 4 HP and takes damage the same way a ward does.
I am following the philosophy that "immobile champions should be much better at whatever they're supposed to do than mobile ones".