Threshold is only one part of the equation, 5k is also largely determined by vvo2 as well. By running threshold sessions 2-3 times a week where does that leave you in terms of the rest of your training? You won’t have time to fit anything else in.
Threshold training does a fine job boosting vo2max and running economy at vo2max paces. It might not be optimal but it is close enough for a base phase before you do 6-12 weeks of more race specific work.