This is probably best explained by first showing an image:
Notice what I boxed for each of the capstones?
Ideally, each of the brother skills, as listed on the capstone, should be the no-brainer choice for that line - at least, if everything was actually working as intended (hint: it's not).
The assessment of the Brother skills as RoR nears?
Self-Shield Brother dramatically improves LoM captain tank survivability, so that was a huge buff to that trait line. A LoM captain will run Shield Brother all the time, and if they don't, they risk going **SQUISH**.
LtC got a pretty good DPS buff from the self-Blade Brother. A LtC captain will run blade brother the vast majority of the time, with the option to sacrifice DPS for group survivability (which fits with how the class works).
Then there's HoH - I would wager that most captains you speak to would say that Shield Brother is a better healing tool than Song Brother, and because of that, the majority of HoH captains are not getting a self Brother. I mean if we're all basically saying:
Instead of 100% (or at least 90% of the time) like the captains would say about LoM/Shield Brother and LtC/Blade Brother, then something is wrong with Song Brother.
Thus, if LoM and LtC got buffs from the self brother skills, and HoH effectively didn't (as observed by play, because Shield Brother is a better healing XBro than Song Brother) - in effect, HoH stagnated, while LtC and LoM were buffed. So two went up, while one stayed the same. Or put a different way, one got nerfed and the others didn't.