If he mixes FOH, then what was he using IEM's for? How loud was he listening? Since he was only listening, would you say that his opinion would be the same if he was one of the performers? Were the Salnotes being driven by a wireless belt pack in the same way that the Roxanne's would be in their intended use?
Generic earbuds often sound squished to me, especially compared to customs.
It won't sound even close when compared in a professional setting with professionals (an arena stage with an arena sized PA system playing at the same time). A $20 IEM won't give the seal (sorry I'm saying it again) and won't stand up to the same abuse that customs have in the live environment. Alternatively, the Roxanne's are not meant for the studio (even if someone advertised them that way) and they will be ineffective in a studio application . So they are two totally different things meant for different applications. Rather than the live sound environment masking problems, I would say that live sound environments present a lot of different problems and different priorities in IEM's. So for people who mix monitors in a live environment, the Roxanne's would be chosen pretty much 99% of the time over any non-custom earbud.
Since you're speaking from the pro audio world, my thought is customs are probably mandatory on stage from a utility perspective, you simply don't want them coming out or loosing seal in the middle of a performance. Personally, I didn't really get what seemed to be better isolation against some of my better fitting universal IEMs in a noisy office environment, probably due to acrylic shells having some ability to transmit sound. Silicone, for sure though, but those are possibly bad for stage use due to difficulty putting in and taking out, esp. as they heat up as a performer moves around under bright lights.
I'm also of the mind that the typical harman targeting, single driver chifi IEMs are almost certainly better from an actual audio perspective, and that frequency response and distortion figures largely tell what you need to know about performance. Many of these have been instrumented on this site to show excellent performance. These companies are approaching this as an engineering problem, which it is. Everyone, regardless of application, should aspire to have Genelec in their ears and some of these get awfully close for the price of a steak dinner. After being in the head-fi scene for ~15 years, probably blew over $50k on it, my take is the number of drivers in an IEM is more a marketing exercise now. Before instrumentation became popular in recent years I do believe these companies in good faith felt there was an engineering aspect here, but at this point it's dubious at best and all golden ears fallacy stuff.
Making distinctions about what is for stage vs studio vs home AFA actual audio performance seems to me to be a bit of a shell game. Some members on this site have Genelec and Neumann in their living rooms because they're excellent. All these pro audio CIEM companies marketed heavily to the head-fi community and probably made the bulk of their revenue from that market - not unusual to find members with collections of $20k+ in CIEMs. Many members would buy whatever was the new hotness every 6 months or so. 1000+ page threads on $4k CIEMS are not uncommon there. These companies clearly made claims about each successive high end models pushing the audio envelope for home use, happily latching onto common audiophile jargon to push product. They all had booths at the national and regional shows, sponsorships on head-fi, and representatives actively involved on the head-fi forums usually on a daily basis. Pre-market announcements, presale discounts, etc. I personally met and chatted w/ Jerry Harvey at a CanJam many years ago.
For stage use, I'm unsure what an artist is getting by spending more in this space beyond some well measuring, lower end customs. Bigger touring acts of course will have no problem kitting their band out with $10-20k in high-end custom sets because they're going to want what is the 'best', but even if the audio is a bit better it seems the volume levels on stage (both ambient and in the IEMs themselves to combat ambient leakage) will just compress things anyway to the point where it's moot.
To be clear, I feel there is a huge distinction to be drawn between the pro audio community in the headphone/iem space vs the speaker space. The speaker companies are serious about engineering in a way that is lacking when it comes to stuff that goes on or in our ears. We've seen this bear out many times over on the products tested for this site. This particular review exemplifies this.