When considering hiring or adding to your team consider what the output per person on your team is now, and what the output per person will be once you have completed the successful addition of the new person to your team. Output per person, not output of the team.
If the output per person remains the same, or worse, is lowered, don’t add. Only add when the addition is a multiplier of output per person. Add this validation to the completion of the addition. Test it. Make sure the hypothesis was and is correct. If the validation isn’t achieved fix it. Don’t accept it.
And, regardless of adding or not, test what you have by working backwards. Examine the output per person on your team as it currently stands. If you had one less person would the output per person decrease? It not, you have a problem with the productivity of the team you have. Fix that before you considering adding anything else.