Art is the right word to describe those older designs. By intuitive feel and a lot of trial and error a few people could build very good TLs. But there were more failures than successes.
Now with the computer design tools available, a TL can be designed on the computer and perform as predicted. No more myths or snake oil, an understanding of how a TL works and what trade-offs are available is easily accessible. The accuracy of TL design is on par with the bass reflex and sealed box enclosure designs. Measured results correlate with the predicted response. The calculations are more complicated but the rewards/payback are greater.