Though I agree that Yoimiya isn't as powerful as Hutao or Ganyu in terms of damage potential for single-target damage, she isn't entirely bad. You need to have better off-field damage dealers like Xingqiu or Fischl and insert one anemo character to shred elemental resistance. All it depends on how you approach your team building and benefit from elemental reactions to deal massive amounts of damage. I've seen some players building and even crowning Amber to run melt or reverse melt teams, and the results weren't bad. I'd advise you to go through your characters and see which characters can synergize well with Yoimiya. And after that, equip them with optimal weapons and artifact sets.