I think that's rather hyperbolic and pretty unhelpful in this context. Many people are well served by the SE215, and by most measures, it can generally be described as a "good" or "decent" IEM at its product line tier, price point and for it's designed uses. It's an unfortunate bent of forums that hype and buzz from a handful of the most vocal members drown out comparative reason and create the appearance (and ultimately "forum fact") that because X can be judged, often on subjective bases, better than Y in some aspect or aspects, that this means that Y is necessarily bad and should be run down.
Most of the chi-fi IEMs are designed for general/consumer use. That some have found favor and been adopted for use in live music performance as entry-level, ultra-budget choices is just a happy coincidence. That various chi-fi IEMs are necessarily, hands-down superior to the SE215 for live music is simply an opinion, and I believe in broader terms than forums or youtube videos, it's a minority opinion, and further, where some objective measure apply, it's not arguably supported by facts.
Fit is a subjective matter, but it's very high in terms of relative importance pretty much across the board...it doesn't much matter how particular IEMs sound if they don't fit or are uncomfortable, and fit also can impact performance. The SE215 has a relatively small shell and small diameter nozzle. In being "universal," these aspects give them a better chance of providing a good and comfortable fit in more ears than the larger, large nozzle KZ ZS10. Does this mean that no one will find the KZ to be comfortable or even prefer its fit? No, it means that more people will find find the Shure to fit better and potentially work better on that basis. Personally, while I don't find the KZ ZS10 shape to be flatly uncomfortable, I find that relative to Westones that are similar in form factor to the Shures (both shell and nozzle size) they are bulky and constantly felt.
By design or by happenstance, the relative levels of isolation impact performance. Again, this can be a subjective matter with objective aspects. One source I found puts the measured outside sound reduction at -24.6 dB for the SE215 and -16.5 dB for the KZ ZS10 Pro. That's quite significant. And further, isolation varies with frequency, and in lower frequencies, the KZ's rejection of outside sound is virtually non-existent (only -2 dB). This means that the sound profile is going to fundamentally change based on the level and type of outside sound. Because live music limits the ability to closely A/B IEMs, listening to recorded music is a typical comparison method. These different levels of isolation have very different impacts on comparison made when listening to recorded music in a quiet room versus a stage with amps and drums in a room with a PA.
The unavoidable fact is that to approach the same relative levels in stage use, the KZ will have to be run at a higher level, which is opposite of the usual goal of minimizing IEM levels and in my opinion pretty much eliminates potential sound quality differences in listening to recorded music. As with fit, this does not mean that no one will adjust to, work with and feel well served by that level of isolation. Actually there is the perfect setup for this to happen. For me, it's easy to envision that many people become enamored with some of these IEMs because of recorded music listing comparisons, reviews (based on recorded music listing comparisons) and forum hype (also largely based on recorded music listing comparisons), that by the time they are using them to play live music, they are simply primed to hear them as being awesome and they end up not realizing that the lower level of isolation is actually forcing them to run at a higher volume.