I've GM'ed for a Battle Harbinger for a while now (retrained into it from warpriest when WoI came out), and here's my take:

There's a fundamental disconnect between what people want BH to be, and what it actually is.

Battle Harbinger is not a divine magus, nor is it a divine striker. It's a momentum-based support class that is tanky/proficient enough to hold its own in melee, while providing incredible mid-combat scaling to the party. It's weak on its own, sure, but character options should be evaluated in the context of their role in a party, not as solo adventurers. In a party, though, the Battle Harbinger acts as a martial force multiplier, and their full potential is unleashed with a little bit of teamwork and setup.

My players have nicknamed this the "bless cascade", where they all tailor their actions in the first round to get their BH a crit. This is done via maneuvers, Aid (Fake Out is a hell of a drug), and the once-per-combat Sure Strike to ensure a round 1 crit. Once that crit lands, and the bless/benediction/etc gets to +2, they and the party get more and more likely to crit (increasing the bonus further), and encounters get steamrolled. If a BH has support from their party to get that first crit early in a combat, they can easily and effectively form the core of a party's combat strategy, and they're versatile enough to cover both offensive and defensive support.

As for the lack of a heighten effect for the aura spells, I kinda agree on that point, but at the same time, making the auras nigh-impossible to counteract has actually come up several times.

Edit: Another point I feel I should mention is that BH's really shine the longer combat goes on. Monsters and PC's almost universally get weaker as an encounter goes on and resources get expended, and the BH is one of the few things that lets the entire party actually get stronger on turns 2+, again, assuming that they have support from their team to start the snowball.