Keqings burst is a DPS buff because she gains 15% Crit for 8s after using it (among ER)
The AoE is decent and its proccing reactions multiple times
You need/want to add someone like Xingqiu to Electro Keqing, or Superconduct to physical Keqing.
Xiao doesn't work with Xingqiu unless you animation cancel and use autoattacks in between each plunge attack for example.
It's all pretty much about the team and not just about a single character for many of those.
Xiao and Ganyu are "solo DPS" most of the time. Ganyu can't proc anything related to normal attacks because she is constantly using charged attacks.
Xiao can but not as frequently as others and Swirl reactions are weak compared to Overload and Electro charged.
Keqing's burst itself isn't weak either, it deals 750% dmg with just one button and unlike Xiao, she doesn't have DPS downtime and can regenerate energy all the time since her E deals decent damage and has a very low cooldown (the damage is especially good with C1)
That is especially useful for your team which will regenerate energy even if they don't use their own low damage E's.