So I have run a gnome light repeater pure arti build a few times in the past couple of months. I don't get outrageous numbers at end game. It's an int build and uses endless fusillade. What the heck am I doing wrong? Where is all this out of balance coming from that people talk about? Basically, what did I do wrong to make mine so sub-optimal?
RXB's used to have 1/3rd doubleshot. Now they get full doubleshot. Expanded clip was changed to grant +33% Doubleshot instead of a 4th shot. Attack rate was also slowed somewhat, in theory to balance this but in practice not quite.
Specifically though, this turned out to be a huge buff for active attacks, and a general buff for normal attacks; at the cost of feeling clunkier for most people. DPS is up, QoL is down. Patience (+1 crit multi for -10% Attack Speed) is also more +DPS for low cost on many/most Repeater builds AFAIK (since many are overcapped on AS, it reduces your actual shots/minute by less than 10%).
Are you using Fatesinger strike? If not, have you tried? It's by far the easiest way to get solid endgame numbers that I'm aware of, on ranged builds. Shiradi T5 + mantle (use Stay Loud), Fatesinger for strike (get T1 sonic vuln and T3 double-sonic-damage), and whatever 3rd tree your build needs (SD is common for SA dice and Evasion, but Machro or others can be more relevant to you).
Otherwise, proc effects like Dripping with Magma (available most easily via Demon Engine runearm, but there are other ways) plus like Bound Elemental Ring of Acid - these all add up fast. On top of the usual Doubleshot, Ranged Power, Int, Deadly, Seeker, Deception, etc.