LOL, I love me some bass, and have been through more than a few sets that possess highly articulate, slammin bass, so it's not like I gravitate towards sterile sounding phones or anything. I can't comment in regard to the JH13 as I've never heard it, but from opinions of those whom I trust, it's a U shaped phone, not exactly neutral. The issue with the Z5 IMO is that it straight up lacks edge, bite and transparency. Guitars just plain sound wrong. I'm not the only person to hold this opinion in this thread either:
http://www.head-fi.org/t/733404/sonys-new-2014-flagship-iem-xba-z5/525#post_11066669
It sounds far from perfect IMO. To be honest, the Z5 disappointed me greatly from the moment I took it out of the box to the moment I sold it. I just never voiced my opinions cause I don't really enjoy coming across as contrarian in a thread of ardent fans, nor do I really enjoy arguing over the merits (or lack thereof) of phones with people who don't see eye to eye with me. I’m just offering my dissenting opinion so that perhaps others with similar tastes to myself can make more informed decisions.
As for what I feel it excels with - as a few others have noted, the Z5 is good with pop, dance, and electronic genres. I believe the Z5 was developed in tandem with a pop music producer or artist so it shouldn’t really come as a surprise that that’s the genre it excels with. As I'd mentioned before, these will appeal to a select group of people, and the very mixed reception in this thread corroborates this.
I also don’t share the opinion that upper mid/treble presence translates to brightness/aggression. It certainly can, but not always. It’s simply not a binary choice of, like upper mids/treble? Z5 no likey. Like relaxed upper mids/treble? Z5 FTW. There are plenty of other phones that I find polite or relaxed in the upper spectrum such as the ASG 1 Plus, LAB I, Tenore, Rockets, SM64 etc. that didn’t set off my alarm bells in the way that the Z5 did.