Are people still swapping into breath sets? If so is the JSE neck better than the one listed on Ryan's guide?
JSE neck in this case is referring to Dragoon's collar and its wyvern lvl+1 effect? If so, the short version is,
Are people still swapping into breath sets?
Yes.
Are people still swapping into breath sets? If so is the JSE neck better than the one listed on Ryan's guide?
No.
Long version.
For elemental breaths, Dragoon's collar isn't going to do anything at all unless you're full timing it. Ele breath dmg is based on current wyvern HP, so increasing wyvern max HP without recovering the current HP will have no effect on ele breath dmg.
And even then, the wyvern lvl +1 effect adds all of +12 wyvern HP with max wyvern param bonus. Lancer's torque would be better assuming you're not capping non-augment breath+ and doesn't require fulltiming. And if you are capped, Chanoix gorget's +50 WHP would be better. But again would need to be fulltimed.
The best options would be Lancer's torque if breath+ is uncapped without it or if breath+ is capped Adad Amulet for the +20 pet MACC. For reference Ptero Armet+2 will cap non-Augment breath + by itself.
Healing breath on the other hand is based on max WHP, so swapping in WHP+ is valid. But even so it amounts to the same thing. Lancer's torque if uncapped breath+, then Chanoix if capped. Dragoon's Collar's WHP+ is too weak to be considered.