That's why I asked what changes they made. I still value official releases, I've tried them whenever they released for years, as they have cores that I want to use such as the BlueMSX, because the alternative is to use the older standalone version and it feels its age to me.
My problem mainly resides in how the interface is and the issues I find every time I want to try it.
I already mentioned the locking yourself out of navigating when wanting to do something as simple as change controller (which HexaEco does on the fly without you having to do anything), or the fact that it simply doesn't recognize other controllers (let's say going from GC to CC), but I also had problems such as trying to make per-core configurations to actually work, or being able to simply configure the picture as I want.
Or how about the annoyances in how you cannot simply rename the core .dol files. I usually have copies of the same core for emulators that can do several systems, so each one has its own config because each one needs its own resolution and such, specially GenPlus GX. If you try to rename cores, they aren't picked up when you try to load "content" (a.k.a. games). Retroarch knows they're cores, you can load them from the main menu, but at the moment where you try to load a game (where, for some reason, you have to load the core again) it's like it's not there. It says there's no core available, asks you to install one, you try, nothing happens.
I tried messing around with the info files to see if it was that but I got nowhere. It could be a way but the cores need to be named exactly as the are. So that's another issue to me.
Just like how divided options are, even for a single element like video options. It makes it far more tedious that it needs to be, going through several menus for doing what would be one particular action. And I also found that trying to change video resolutions sometimes do not have any effect on the picture output, you need to use a different vertical resolution to reset it and go back to the one you wanted to use, or changing one option there actually resets another option there, and now you have a super stretched picture horizontally.
And I was one of those weirdos that stuck with official 1.0.0.2 for years because of the better performance over later releases, even when you had to set the aspect ratio every time you changed cores, mind you, I'm no stranger to set up things constantly. But that's a choice I made consciously, not something I'm forced to deal with every time and shouldn't work like this.
This was my last experience a month or two ago, and looking it seems like it is still the latest version. And like that many other attempts, every time I spend hours trying to set it up to be decent but I just end up feeling like I'm bashing my head against a wall. And I know that this is the experience quite a few people have with RetroArch as a whole, on other devices too, I've read constant complains for years.
I am happy that the cores are seemingly improved, because older official releases had big issues like save states crashing the app and such. I was very excited to see the Picodrive working so well out of nowhere or when they get new features. I really want RA to be good because it's a door to play so many fantastic games and a lot of people work on both the front end itself and the emulators. I still have appreciation to official releases.
The interface just "kills it" for me. This is why I stood with RA-Hexaeco. The changes to the interface make using it so much more straightforward, so much simpler to set up, so much less hassle... I get to enjoy RA without the problems I find, even if it doesn't have every feature the official ones have (although it has some exclusive to it).
I still have some solitary cores on separated folders for things like SNES MSU-1 or the already mentioned Picodrive (or Virtual Boy, to see if new releases manage to fix the slowdown) but man, it really is sad and frustrating to me. I don't like being negative, but that has been my experience with official releases for quite some time.
...About mGBA, what does it make better on RA than standalone? Because, I remember testing myself and some games that would have frame drops in RA or RA-Hexaeco ran well on standalone. For the most part the RA cores work nice though, and as always when comparing standalone emulators and RA cores, a well configured core gives a slightly sharper picture, so I still find myself using HexaEco's mgba core often.
About CHD, it's nice certainly. I don't know how much it lowers the size (haven't tried that format much myself) but any way to cut down CD game sizes is really good, specially here with SD cards as the main storage device.