I just tested this guy out and it is quite overpowered. With a base melee damage of 100 its range is actually 100-800 per attack. Not sure if you know the formula for damages, which I did not either until recently, but you can see it
here.
The few times I got hit from this guy I died instantly, with full armor.
I feel that this monster is also way too fast. Not only is it very hard to keep track of and even shoot the monster it also looks poor in-game. With how fast it moves around an area it constantly jumps from one place to the other, making it look very choppy, feel pretty low quality, and gives the impression of lazy implementation of a speed mechanic without any form of making it visually appealing. Additionally, it feels cheap because of how fast it moves around and how much damage it deals. In tight corridors or rooms it is really difficult to keep track of the monster and before you can even lay your eyes on it its already killed you. I understand that this is suppose to be an ambush enemy that focuses on quick and powerful strikes, but the way it is implemented feels very unfair and poorly executed.
There are other ways to make a fast and powerful monster than just boosting its speed and damage stats. When I read your latest post you mentioned
when it runs at the player, it should close the distance quickly, and maybe make them jump a bit.
which I thought meant that the monster would actually jump in the air towards the player to close the distance, like a leap attack or something. That mechanic would be perfect for a speedy monster because it could leap long distances very quickly and suddenly. I'd personally recommend finding mechanics that would make the monster speedy but not at the cost of visual appeal.
I do like the idea of a glass-cannon type speedy enemy though. But in its current state it's a bit unfair with how overpowered it is, even with its health being as low as it is.