Right now you have long, straight primary branches without movement or taper and the main branching is all at the end of your primary branches. A tree with a thin trunk looks leggy with this kind of branch configuration. Also, long term, it will only get more leggy because there is little on the interior to cut back to. In my experience, these interior locations on older wood are very difficult locations on which to encourage backbudding. It may be that you will need to consider grafting shoots to these locations. Grafting is a common technique on black pine to produce new shoots on old branches, correcting leggy growth. I have trees with dozens of grafts, some of which are now the primary branches. I’ll probably graft several dozen more scions this coming spring - I graft almost every season.