I equipped my follower with a weapon socketed with a ruby. In the tooltip it said it is lower in DPS, but when I equip, the DPS is higher. I think the tooltip doesn’t count the gem.
Could you fix it?
First, this is not a technical issue and won’t be handled by technical support. You should report it on Bug Report forum: https://us.forums.blizzard.com/en/d3/c/bug-report/23
Second, this is a known fact and has been reported many times. I don’t think Blizzard will fix it because it is not a game breaking issue. Equip the items to get a more precise sheet values.
Third, the DPS followers are negligible. No one cares about their DPS at all. We only use their special abilities.
If you want to compare items without considering socketed gems and/or Caldesann’s Despair applied to them, hold down Shift whilst hovering the mouse over the item to be compared.