I feel curious: Which emulator do you think is not a mess? The retroarch core? The one called
"Play!"? AetherSX2? Or maybe... DamonPS2? (*heaves in malware*)
AetherSX2, the best of the list, isn't better than PCSX2, it matches it, because they share most of their code. Play! is unripe (unsurprisingly, made by a single programmer, although its HLE BIOS is an archivement). DamonPS2 is unstable buggy crap.
Face it: All emulators look like messes to you because the hardware they try to emulate is a total mess (a wonderful, yet crazy mess). that can't be translated well to modern PCs.
The code of the games is usually a similar mess, relaying in racing conditions, disk timings, undocumented HW bugs, subpixel accuracy that breaks scaling, the interlacing...
PCSX2 team, with less developers than Dolphin's, has done a quite amazing job emulating PS2... and in the last years they had done huge improvements and modernization (code clean-up, plugin merge, improved OpenGL and D11, more stable MTVU, hacks removal, QoL...) and with a lot coming soon: The 64 bits version is almost finished, they're working in a OSX port with Metal, a new QT interface...
If it's not enough for you, you can develop your own emulator.
- Vulkan has some perks, but they're not enough to make it overwhelming superior and a priority for PCSX2 team.
- Every new alternative mode means more work for devs: writing it and later maintaining. Making Vulkan as good as the other modes would take effort and time, time the team couldn't dedicate to fixing bugs or adding other kind of features.
- They thought a decent Vulkan mode would require VK_EXT_fragment_shader_interlock, an optional extention AMD refused to implement in their drivers, so they wouldn't consider working on a Vulkan mode until AMD changed their mind. (Luckly, Stenzek found a replacement to that extension)
- Since Vulkan is a more recent, less popular API, during the first years there weren't many devs familiarized with it.
