I got my Lunas within days of Audyssey releasing their MultEQ app for recent (2016 and later) model receivers, allowing Audyssey Pro-style tweaking from your phone. I took the opportunity to re-calibrate my setup with new Luna surrounds to go with my Sierra 2 LCR.
You need to know what you're doing a bit more, but you can correct for things Dave pointed, like speaker capabilities, and even set the freq cutoff for EQ to EQ only bass, where room correction actually makes sense. You can even see that Audyssey does try to figure out speaker capabilities and defines a target curve that rolls off in the bass differently for speaker groups. It can get this wrong though, and being able to tweak the target based on known speaker capabilities is a huge help to the final result.
I've had differing experiences with Audyssey (and auto eq in general). What I've found:
1. Newer systems keep improving in both how they measure and quality of results. XT 32 does much better with subs and the measurement stage will now redo the initial sub measurement at different volume if too high/low to be accurate.
2. It's on the user to place the mic well. Audyssey now recommends a tight grouping for multiple measurements. Start with primary position, and all other measurements should be within roughly 2 feet. Doing all 8 measurements on a tripod yields best results.
3. Bass is a huge part of overall sound quality. You should get/borrow an SPL meter and just play around with moving your sub(s) and measuring tones. Always set up your sub the best you can before running auto eq. Same goes for speaker placement (especially if running full range) before running EQ.
4. MultEQ app let me tweak things and avoid EQing high frequencies. It also allows disabling the midrange compensation (BBC) dip designed to fix crossover issues around 2khz. I've never had issues with an Ascend speaker in any freq range and so I disabled this dip. By the way, what is the crossover freq for the Sierra 2/Luna? This got me to the point of not feeling the need to disable Audyssey for music. In fact, I now prefer it enabled.
Personal preferences:
1. Audyssey Dynamic EQ works far better than any loudness control I've ever used and makes low volume listening just as engaging as reference level. In theory, it makes anything below reference level more accurate and faithful based on human perception of frequencies at varying volumes. So I don't see it as a gimmick, but actually the most correct way to listen.
2. Audyssey Dynamic Volume is way ahead of old night modes and is much needed (at the lowest setting) for movies in my 50s built San Francisco apartment. I of course don't use it for music.
By the way, the Lunas are practically overkill for surrounds, but the seamless blend with the 2s is oh so nice for everything from movies, to video games, to multichannel music