Xerath's ult is very unsatisfying to use; the current change to 3/4/5 shots and reducing its base damage doesn't help either.
To begin, let's see what the description says: "Xerath immobilizes himself and gains numerous long-range barrages." Google defines "barrage" as "a concentrated artillery bombardment over a wide area" but Xerath's ult is certainly not a concentrated artillery bombardment (because of its very limited amount of ammunition) and feels more like 5 lame shots.
My suggestion is to change Xerath's ult to something similar to the Ascension Xerath Bot's ult, fire many shots in rapid succession for a decrease in damage. Perhaps have like 25 shots that can be fired over a duration of 10 seconds with a maximum fire rate of 5 shots per second. Each shot can do around 50/75/100 damage (+10% AP) and holding down R will fire the shots at maximum rate. I feel like a change to have him fire more shots would be more interesting and would feel more like an actual barrage rather than a lame five small hits. Additionally, it would be nice if the zoom out would zoom out further to encompass the entire area it covers because having to unlock a camera that is already zoomed out is a real pain.
I hope you guys will agree with me as I feel like this would be an interesting change.