Here's the problem with this. Tracking is a waste of a perk. Proximity is the better perk option because tracking still has to direct impact the target. You're making dragons breath the same with a waste of a perk, and not touching gjallarhorn in any way. In the grimoire for rocket launchers, it literally says that skilled users will aim at the feet of enemies. Doing this negates any need for tracking. Proximity allows you to basically have the same effect as shooting their feet, but with not actually having to shoot there. Increases the size of your target massively in essence. Your so called fix doesn't help balance gjallarhorn or make dragons breath any more useful.
I understand your point, but I think you're mistaken- with the new reduction in the effective range of the prox det perk, that will serve to also make that perk less desirable, requiring additional skill to dumb-fire the rocket close enough to get it to proc.
Also, for long-range encounters, especially, tracking is superior because it both ensures a hit on a moving target, as well as causes additional damage due to the impact.
Prox det rockets actually do less damage to a single target because they do not actually impact it.
Finally, specifically for the Dragon's Breath, prox det would not help it achieve maximum DPS because of the relatively small radius of the solar flares.
That is why I thought those perks should be divided up how I listed them.