Honestly you don't use repeaters till at least L12, inqui is just more efficient and you get Ratty which doesn't have a comparable RXB counterpart. RXB is usually overkill against early content, DXB lets you move faster
Once you get T5 then there's more value to RXB and rotating your three AoE shots. Or even waiting till L20 when you start getting things like FS strike and Hunts End that really leverage being tripled
But if you want to use RXB to level just on principle, a Keen xbow probably outweighs everything else till you get Imp Crit, and there aren't any named ones till L13, so CC a double slot base, add Ghost Touch and a Snowpeaks ruby, and just keep upgrading with Xd6 acid ruby as you level
At 16/20, Nightshade Venom is probably the most useful effect since it gives you one hit of helpless when it procs. You can just ride that to cap if you don't have a Needle to upgrade to.